Apparatus and method for supercritical fluid extraction or supercritical fluid chromatography

ABSTRACT

An automatic variable-orifice fluid restrictor for use with a supercritical extractor having a collection trap or a supercritical chromatograph includes an inlet line for fluid at a pressure above its critical pressure, an extended tubular probe having an inner and an outer surface and a proximal and a distal end. The proximal end of the probe carries an inlet connected to the inlet line and is outside of the trap. The distal end of the probe includes a variable orifice means adapted for metering the fluid. The variable orifice means is adjacent to the outer surface of the probe and is located in the midst of the trap. The variable orifice means is adjusted by an adjusting stem having first and second ends. The first end of the adjusting stem is connected to automatic control means such as a servo at the proximal end of the probe and outside of the trap. The second end of the adjusting stem varies the area of the orifice by moving a first orifice member. The stationary second orifice member cooperates with the first orifice member to form the orifice. The first orifice member moves axially when the orifice is closed and moves both axially and rotationally when the orifice is open or partially open. This cleans deposits from the orifice without damaging the orifice parts by high pressure notional physical contact.

RELATED CASES

This application is a continuation of Ser. No. 08/382,650 is acontinuation-in-part application of U.S. patent application Ser. No.08/096,919, filed Jul. 23, 1993, now abandoned, which is acontinuation-in-part of U.S. application Ser. No. 08/027,257 filed Mar.5, 1993, now U.S. Pat. No. 5,268,103 which is a continuation-in-partapplication of U.S. application Ser. No. 07/908,458 filed Jul. 6, 1992,now U.S. Pat. No. 5,198,197, which is a division of U.S. applicationSer. No. 07/795,987, filed Nov. 22, 1991, now U.S. Pat. No. 5,160,624,which is a continuation-in-part of U.S. application Ser. No. 07/553,119,filed Jul. 13, 1990, now U.S. Pat. No. 5,094,753, for APPARATUS ANDMETHOD FOR SUPERCRITICAL FLUID EXTRACTION.

BACKGROUND OF THE INVENTION

This invention relates to supercritical fluid extraction andsupercritical fluid chromatography and more particulary to thecollection of extracted or separated sample in supercritical fluidextraction or supercritical fluid chromatography.

In supercritical fluid extraction, an extraction vessel is held at atemperature above the critical point and is supplied with fluid at apressure above the critical pressure. Under these conditions, the fluidwithin the extraction vessel is a supercritical fluid. In supercriticalfluid chromatography, a similar process is followed except that thesupercritical fluid moves the sample through a column, separates some ofthe components of the sample one from the other and removes thecomponents from the column.

In one class of supercritical fluid extraction of chemical componentsfrom a sample using a supercritical fluid, the components dissolved inthe extraction fluid are separated from the fluid for further analysisby allowing the extraction fluid to vaporize.

In a prior art type of supercritical fluid extraction apparatus, theanalyte precipitates on the surfaces of the expansion device, such asfor example, along the walls of a linear capillary tube restrictor or onthe walls of tubing beyond the limiting orifice of a point restrictor asthe extraction fluid vaporizes. Commercially available metering valvesas point restrictors require the analyte to be removed from the internalsurface area of the connecting conduit or in tubing downstream from thevalve in which it precipitates.

The analyte is collected in a trap such as a collection solvent,granular absorbent or chilled inert granular material located in acollection vessel. In the prior art, one key advantage is achieved bycollecting the analyte in collection solvent within the collectionvessel which advantage is that volatile analytes are less likely to belost by their own vaporization and that low volatility additives or"modifiers" of the supercritical fluid do not wash analytes from thistype of trap.

This loss occurs because, as the extraction fluid vaporizes, volatileanalytes may also tend to vaporize and be lost with the extractionfluid. By collecting the effluent in supercritical fluid extraction andin supercritical fluid chromatography in a collection solvent cooledbelow room temperature (e.g. 0 to -20 degrees C.) it will be dissolvedin the collection solvent rather than being lost with the expandedsupercritical fluid, which is a gas after expansion. The higher recoveryrate of volatile analytes is advantageous when the content of volatilecompounds in the sample is small and when the volatile content is to bequantified.

The prior art apparatuses and methods for collecting sample have thedisadvantages of requiring an excessive amount of time and equipment toremove analytes from tubing and of losing some analytes. They have thefurther disadvantage that analytes precipitating in the expansiondevice, also called a restrictor, change the flow properties of thedevice and therefore change the system flow or pressure. This causesirreproducible extraction conditions. Prior art expansion devices mayalso plug tightly, prematurely terminating the extraction as well asbeing a maintenance problem.

In collecting sample (analytes) during supercritical fluid extractionand supercritical fluid chromatography, a fluid flow restrictor isincluded to maintain high pressure in an extraction chamber or columnwhile allowing a controlled flow rate through the sample beingextracted. One type of restrictor is a length of small internal diametertubing, often referred to as a capillary restrictor or capillary.

To avoid freezing or deposition of water or other extracted substancesdissolved in the fluid on the wall of the tubing, the capillary isheated. The need for heating is especially great when using a coldcollection trap comprising a cold collection liquid solvent in which theoutlet end of the capillary is immersed and through which gasifiedextractant is bubbled.

In one prior art heated restrictor, the capillary is heated by thermalconduction along its length and by heat or enthalpy added to the fluidwithin the capillary, which moves along with the fluid flow to theoutlet end of the capillary. The fluid discharges into a cold, dry tubeof relatively large inside diameter. This larger tube then dips into thecold solvent trap. Ice and analytes build up on this tube but do notplug it because of the large diameter. This is described ininternational patent application number WO 92/06058, dated Apr. 14,1992.

This arrangement is disadvantageous because it is often difficult toremove analytes solidified on the inside of the large tube for assay.

It is known to directly resistance heat a member and to control the heatwith a feedback system using the electrical resistance of the member tomeasure its temperature and compare it to a reference temperature. Thistechnique is taught for use in a gas tube by U.S. Pat. No. 4,438,370;the disclosure of which is incorporated herein by reference.

Needle valves used as restrictors are either of the rotating stem typeor the non-rotating stem type. Automatic restrictors change their stemposition very frequently because of their servo control. Rotating stemrestrictor valves are seldom used as automatic restrictors because oftheir very short rotational adjustment life at high pressures, due togalling or other destruction of the mating fluid metering parts. Forthis reason non-rotating needle valves are commonly used as automaticadjustable restrictors. This type of restrictor has a tendency to plug.

In another restrictor-collector system that may or may not be prior art,a heated variable restrictor is mounted within a heating block. A tubeextends from the heated variable restrictor into the collection trap.This type of variable restrictor may still have the disadvantage ofdepositing extract on the tubular walls of the tube that extends fromthe heated variable restrictor into the collection trap. A system ofthis type is described by Maxwell, et al. in "Improved SFE Recovery ofTrace Analytes from Liver Using an Integral Micrometering Valve-SPEColumn Holder" The Journal of Chromatographic Science v. 31, June 1993,pages 212-215; Journal of High Resolution Chromatography, v. 15,December, 1992, pp. 807-811.

Hoyer in "Extraction with Supercritical Fluids: Why, How and So What",CHEMTECH 15, 440-448, (July 1985) discloses an arrangement wheresupercritical fluid leaves the extraction vessel and is led to apressure letdown valve (restrictor). After leaving the restrictor, theanalyte is collected in a collection chamber or trap. A supercriticalfluid pump controls the flow rate and the restrictor valve controls thepressure. In order to prevent valve plugging by deposition of analyte,the author recommends heating the restrictor, and if this is notsufficient or feasible, to use a restrictor valve designed so that itdischarges analyte directly into the collection chamber. Currently thisis the earliest known reference to discharge of analyte from a valveorifice directly into the collection chamber. However there is nomention of constructing the restrictor valve as an elongated probe thathas its orifice in the midst of the chamber nor is there any suggestionof a self-cleaning valve.

Nickerson, et al. U.S. Pat. No. 5,009,778 also discloses a valve andtrapping assembly in which the restrictor valve is designed so that itdischarges analyte directly into the collection chamber. There is nodisclosure of self-cleaning during an extraction to remove analytedeposited in the orifice nor of an elongated probe design.

Saito, et al. in European Application No. 88100485.7 discloses anautomatically adjustable restrictor for supercritical extraction havinga valve stem which is continually moved or vibrated reciprocally. Thiscleaning action resulting from this motion is said to prevent adhesionof analyte to the metering or orifice area. In some publications it hasbeen said that this vibrating action has a self-cleaning effect, whereasother commentary indicates that this type of restrictor still does plug,perhaps due to the reciprocating or vibrating action of the valve stempounding or tamping deposited analyte into a plug in the orifice. Thispatent contains no teaching of the use of an elongated probe so that theorifice can be located in the midst of a collecting volume instead of atthe edge of a collecting volume nor does it teach the combination ofcontrolled, switched on and off, rotating and axial motion of a valvestem for self-cleaning and long life.

Saito in U.S. Pat. No. 5,031,448 discloses a restrictor valve with aninternal wash just downstream of the fluid metering volume. This washingmeans will not prevent or clean out deposits between the two specularlypolished surfaces constituting the metering orifice.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a noveltechnique and apparatus for supercritical fluid extraction orsupercritical fluid chromatography.

It is a further object of the invention to provide a novel technique forreducing the loss of sample in supercritical fluid extraction andsupercritical fluid chromatography.

It is a still further object of the invention to provide a noveltechnique and apparatus for reducing time lost in recovering sample thathas formed a coat in tubing during collection.

It is a still further object of the invention to provide a novelvariable orifice fluid restrictor for use with a supercritical fluidextractor or chromatograph.

It is a still further object of the invention to provide a novelvariable orifice fluid restrictor whose orifice is located at the end ofa long, thin probe.

It is still a further object of this invention to provide a novelautomatic variable restrictor free of plugging and having predictableflow properties enabling reproducible extractions.

It is a still further object of the invention to provide a novelsupercritical extraction apparatus that processes a series of samplesautomatically.

It is a still further object of the invention to provide a novelsupercritical extraction apparatus that can use different sizes ofcollection vials through the use of a variable orifice restrictor whoseorifice is located at the end of a long, thin probe.

It is a still further object of the invention to provide a novelsupercritical extraction apparatus that allows the vials to beinterchanged during the extraction process.

It is a still further object of the invention to provide a novelsupercritical extraction collection apparatus that improves trappingefficiency by controlling the temperature and pressure of the collectionvial and yet is automatically loaded without the need for handling by anoperator.

It is a still further object of the invention to provide a novelsupercritical extraction collection apparatus that reduces collectionsolvent loss by controlling the temperature and pressure of the vial andyet is automatically loaded without the need of handling by an operator.

It is a still further object of the invention to provide a novelsupercritical extraction collection apparatus that avoids plugging ofthe variable orifice restrictor by locating the orifice at the outlet ofthe restrictor with no significant connecting tubing between the orificeand the outlet.

It is a still further object of the invention to provide the location ofthe orifice of a variable orifice restrictor buried within a collectingtrap and not at a side, edge or end of the collecting trap for thepurpose of trapping extracted substances.

It is a still further object of the invention to provide a long-livedvariable orifice restrictor for high pressure fluid having aself-cleaning orifice in which the cleaning action is mechanicallypositive, yet does not require high pressure motional contact of valveparts.

It is a still further object of the invention to provide a long-livedautomatic variable restrictor that cleans itself by relative rotarymotion between valve parts when the valve is partially open andregulates flow by relative axial motion between the valve parts.

It is a still further object of the invention to provide a novelcollecting trap using reduced temperature and elevated pressure for thepurpose of trapping extracted substances but which nonetheless does notcause the restrictor orifice to plug through cooling the orifice.

It is a still further object of the invention to provide a novel methodof maintaining a hot orifice which is immersed in a trap without heatingthe trap.

It is a still further object of the invention to provide a novel methodof maintaining the temperature of an elongated restrictor heated byelectrical and/or thermal conduction along some part of its length.

It is an object of the invention to provide a novel restrictor tubingoutlet end thermally insulated from the surrounding collection solventinto which it is immersed.

In accordance with the above and further objects of the invention, acontrolled variable expansion of supercritical fluid used insupercritical fluid extraction or supercritical fluid chromatography isprovided by a restrictor. This restrictor: (1) permits the analyte,which had been dissolved in the supercritical fluid to be depositeddirectly into an external environment, such as a collection vessel,instead of first depositing it into a connecting conduit that leads toan external collecting vessel; (2) can be used without a connectingconduit; and (3) allows independent control of the fluid back pressureto change the solvating power of the supercritical fluid independentlyof the flow rate.

The restrictor is variable and incorporates controllable metering meanswith at least part of said metering means being movable and controllableby an adjusting means extending out of the region comprising the analytecollection means to effect its said control and with its outlet beingsubstantially immediately surrounded by a region comprising an analytecollection means.

In the preferred embodiment, the variable restrictor is a point(orifice) restrictor as opposed to a linear (capillary tube) restrictor.It produces expansion of the supercritical fluid at the point ofdischarge to a collection system. Frequent incremental rotational motionof a metering stem or needle with respect to a metering seat when thevalve is partially open largely prevents the analyte from precipitatinginside the orifice. Any analyte that does so precipitate is very soonloosened by the rotary action and discharged, providing a self-cleaning,non-plugging and non-fluctuating valve. This relative rotary motiontakes place when the valve is partially open, and not when it is closed,so the sealing parts of the valve are not damaged by this cleaningaction. The variable restrictor incorporates controllable metering meanswith at least part of said metering means being movable to effect itssaid control. The metering means outlet is substantially immediatelysurrounded by a region comprising an analyte collection means. Themetering adjustment is controlled by an axially moving adjusting meanslocated out of the region comprising the analyte collection means.Cleaning is controlled by rotary motion means located out of the regionof the analyte collection means.

The apparatus presented here provides an abrupt expansion of thesupercritical fluid, and controls the location at which the analytescome out of solution to a location near or at the point where the fluidflow reaches the outside environment. This eliminates the necessity ofsecondary flushing of the restrictor and associated connecting conduitto move the analytes from the restrictor system and convey them to theoutside environment.

The novel restrictor includes a metering valve having an adjustablemetering orifice at the end of a long, narrow external probe in contactwith its externally surrounding trap, such as a collection solvent in acollection vessel. This apparatus provides for expansion of thesupercritical fluid or liquid to a gas at an orifice at the tip of aprobe, which can be inserted into a collection vessel. The expandedextraction fluid is allowed to bubble as a gas through immersion in acollection solvent which is preferably chilled and pressurized. Suchimmersion eliminates the need for an easily plugged tubing connectionfrom the orifice to the solvent. Alternatively, it may spray as a liquidor gas entraining a liquid or solid into a chilled or pressurized: (1)empty collection vessel; or (2) inert particle or absorbent-filledcollection vessel. Supercritical pressures are maintained upstream ofthe tip of the probe, preventing the precipitation of extracted analytesin the restrictor.

Regulation of back pressure (pressure upstream of the tip of the probe)is achieved by a variable orifice created at the tip of the probe. Thevariable orifice allows control of the flow rate of the fluidindependent of pressure, and therefore variable control over theextraction process. Once the extraction fluid is allowed to expand to agas, its ability to carry the analyte is lost and the analyteprecipitates. Because this expansion occurs at the tip of the probe, theanalyte precipitates directly into the midst of the collection solventor particulate medium, thereby improving collection efficiency.

More specifically, a variable-orifice fluid restrictor for use with asupercritical extractor or chromatograph includes an inlet line forfluid at a pressure above its critical pressure and an extended tubularprobe having an inner and an outer surface and a proximal and distalend. The proximal end of the probe is disposed toward the inlet line andthe distal end is disposed toward the collection environment such as ina collection chamber or the like. The distal end of the probe containsan adjustable orifice means adapted for metering the fluid, whichorifice means is comprised of first and second orifice members and anadjusting stem having first and second ends.

The adjustable orifice means is located within the inner surface of theprobe adjacent to the outer surface of the probe tip with at least partof the orifice means being movable to effect its said control. Itsoutlet is substantially immediately surrounded by a region comprising ananalyte collection means and is controlled by the adjustable stem thatserves as an adjusting means in the preferred embodiment, extending outof the region comprising the analyte collection means. The adjustingstem has first and second ends, the first end of the stem being adaptedto movably control the metering means and said second end of the stemcarrying a feature which provides for independent control of themetering means.

The orifice means is adjustable by moving the adjusting stem. For thispurpose, the second end of the adjusting stem is located at the proximalend of the probe and the first end of the adjusting stem is located atthe distal end of the probe and is connected to and adapted for movingthe first orifice member with respect to the second orifice member,thereby controlling the adjustable orifice for varying the restrictionof fluid passing through the adjustable orifice. The second end of theadjusting stem extends past the proximal end of the probe and cooperateswith an orifice adjustment control.

To automate the operation under the control of a microprocessor, a motoroperated fraction collector, a motor operated sample source and a motoroperated sample injector automatically move samples and collectioncontainers into an extraction station, inject samples into theextraction pressure vessel, perform extraction and collect extractant indifferent appropriate collection containers in a timed sequence topermit extracting of a series of samples with minimum human handling.

In the preferred embodiment, a movable motor member is aligned: (1) withan opening in a sample cartridge reel that moves sample cartridgescarrying samples into the extraction station; and (2) with an opening inthe extraction pressure vessel. The movable member is dimensioned to becapable of sealing a correspondingly sized opening in the pressurevessel and adapted to move the sample cartridge into the pressure vesseland seal the pressure vessel. Motors are provided to operate the valvesto permit the extraction operation on the cartridge. The movable memberis removed from the pressure vessel after extraction and returns thesample cartridge back to the sample reel.

In operation, the sample to be extracted is placed within the cartridgeand the cartridge inserted into and sealed within a pressure vessel.Upon insertion, one of two outlet fittings communicates with theinterior of the cartridge and the other with the interior of thepressure vessel outside the cartridge. An inlet to the pressure vesselcommunicates with the outlet of a pump which pumps the supercriticalfluid along a path that heats it and through a programmable valve intothe interior of the pressure vessel and extraction cartridge. For eachextraction, the valve is automatically opened by a computer controlledmotor that releases a valve element to permit flow and closes it toprevent further flow.

To remove any contaminants from outside of the cartridge, the outletcommunicates within the inside of the pressure vessel and outside of thecartridge and thus, permits the supercritical fluid to cleanse theoutside of the cartridge and the inside walls of the pressure vesselfrom contaminants as it flows outwardly to a contaminant collector.

For extraction, the cartridge includes an outlet that cooperates with anextractant outlet of the pressure vessel and is connected to thefraction collector so that supercritical fluid flows into the cartridge,out of a fitting that communicates with the interior of the cartridgeand into an appropriate collection container.

In the operation of an automatic supercritical fluid extractor, samplecartridges are disposed in the sample changer and are automaticallytransported to the pressure vessel for extraction by a supercriticalfluid. In the preferred embodiment, this transport is first horizontalin a reel of successive sample vials and then vertical through anopening into the pressure vessel. The transport mechanism seals thepressure vessel and is locked in place and motor-driven valvesautomatically apply extracting fluid first through a purge cycle andthen through one or more extracting cycles to extract fluid. A fractioncollector, which in the preferred embodiment is a reel holdingcontainer, moves the fraction collector containers into position forcollection. In the alternative, extractant fluid tubing may be movedfrom container to container.

An embodiment of collection vial piercing mechanism includes means foradding temperature and positive internal pressure control for the vial.Positive pressure in the vial suppresses misting of the collectionsolvent and loss of dissolved analyte. Excess gas from the vial iscontained and then routed to a remote location for collection anddisposal.

To collect sample, one embodiment of collection system includes multiplecollecting vials partially filled with collection solvent through whichthe restrictor bubbles CO₂ with entrained analyte. Each vial has aslitted septum on its upper, open end to allow passage of the end of therestrictor into the vial. In one embodiment, the restrictor is loweredinto a vial. In another embodiment, the vial is lifted onto therestrictor by a rod connected directly to the extraction cartridgeelevator.

In still another embodiment, the vial is lifted by a vial lifter that isseparate from the cartridge elevator. To permit changing of the vialduring the extraction process, a lift that functions separately from thesample cartridge elevator is required.

This embodiment has the advantage over moving restrictor embodiments ofnot causing wear and breakage of the restrictor by flexing itsconnecting tubing repeatedly. It has the advantages of the embodimentsin which the vial lifter is directly connected to the cartridge elevatorof: (1) allowing the vials to be changed during the extraction processwithout depressurizing the extraction chamber; (2) better trappingefficiency; (3) lower extract/solvent losses; (4) reduced freezing andplugging of the restrictor; and (5) reduced icing up of the outside ofthe vial.

The ability to change vials during the extraction process has severaladvantages, such as for example: (1) it makes it relatively easy tochange the conditions of the extraction, such as temperature andpressure or to remove certain substances from the sample matrix anddeposit each substance in a separate vial; (2) it is useful forinvestigating extraction kinetics; and (3) if a separate lift is used,different size vials may be accommodated since the stroke is no longertied to the extraction cartridge elevator.

Changing a collection vial after an extraction without having todepressurize the extraction chamber makes using multiple wash stationseasier. Wash stations are used to clean the outside of the restrictor.Several vials are used in sequential washes of the restrictor to diluteany possible contamination from one extraction to another to acceptablelevels. Without a separate vial lift, the chamber would have to bedepressurized and repeatedly loaded with a blank for each washing step.

Trapping efficiency and low collection solvent losses can be gained byseveral techniques. One such technique requires reduced collectionsolvent temperature during extraction on the order of five degreesCentigrade or less. However, reduced temperature, while improvingtrapping and reducing losses, may also create problems with restrictorplugging and icing up of the vial. Ice on the outside of a vial mayinterfere with the vial being lowered into the vial rack aftercollection. To prevent these problems, heat must be supplied to the vialto maintain a minimum temperature. Ideally, a system would precool thevial before the extraction begins and then add or remove heat tomaintain this temperature.

To improve trapping and reduce losses, a sealed system is used with aregulator to maintain pressure, and the collection vials are pressurizedsufficiently to reduce the mist containing analyte and vapors resultingfrom the violent expansion of the gas exiting the restrictor in anunpressurized vial and to prevent loss of gas through the vial's vent.The pressure is sufficiently elevated to stop misting and to decreasethe vaporization rate of collection solvent and analyte, and so that ata given mass flow rate of gas, the gas volume and bubble size arereduced. In the sealed system, the gases and vapors may be routed forproper and safe disposal.

To maintain an adequate solvent level, a liquid level control systemwith sensing of the liquid level in the vial may be provided. Thissystem activates a collection solvent replenishment means when thecollection vial loses too much collection solvent due to evaporation.The fluid level sensing system benefits from the pressurized systembecause increased pressure reduces the violent bubbling and this makessensing easier. Alternatively, the replenishing fluid may be addedaccording to a present program, with no level sensing used. This is madepossible by the reproducible and predictable operating conditions thatobtain when using the preferred embodiment of restrictor.

In one embodiment, the collector includes means for receiving the fluidfrom the extractor and supplying it to a collection liquid at atemperature that permits partition of the analyte between the trappingsolvent and the extractant by avoiding freezing of the extractant beforepartition but at a temperature not so high as to cause the bubbling awayof the extract with the extractant. This usually involves cooling thecollection liquid.

The means for supplying the fluid to the trapping solvent or collectionliquid is a variable orifice pressure release restrictor with theorifice immersed in the collecting liquid. To this end, the orifice islocated at the end of a long, thin probe. Because the supercriticalfluid often carries entrained water and because the region of theorifice is cooled through fluid expansion, ice can form at the orificeand plug it. To prevent this from happening the metal walls around theorifice are heated. The probe, especially including the heated area, isinsulated to decrease the heating effect on the cold collection fluid.The heat and insulation minimize the transfer of heat to the collectionliquid while maintaining the orifice which is immersed in a cold solventat the proper higher temperature to avoid freezing or internaldeposition.

As can be understood from the above description, the supercriticalextraction technique has several advantages, such as for example: (1) itautomates the sample injection and fraction collection part of theextraction process as well as automating the extraction itself; (2) itallows the vials to be changed during the extraction process withoutdepressurizing the extraction chamber; (3) it provides good trappingefficiency; (4) it provides low analyte/solvent losses; (5) iteliminates freezing and plugging of the restrictor while allowing thevial to be operated at a lower temperature to increase collectionefficiency; (6) it reduces icing up of the outside of the vial; (7) itpermits the conditions of the extraction, such as temperature andpressure, to be changed such as to remove certain substances from thesample matrix and deposit each substance in a separate vial; (8) itprovides controllable operation and reproducible results; (9) it is alsouseful for investigating extraction kinetics by changing the vial duringthe extraction for examination; (10) it permits the use of differentsize vials because the stroke of a lift is no longer tied to theextraction cartridge elevator; and (11) it permits the use of multiplewash stations to clean the outside of the restrictor.

Heretofore automatically adjustable restrictors or servo-controlledrestrictors for supercritical extraction or chromatography have had aproblem with erratic flow or even plugging. This problem is largely dueto solid analyte dropping out of solution in the fluid as it changesphase from supercritical to gas. This has been partially alleviated byheating the restrictor and having the restrictor valve orifice dischargedirectly into the collecting trap. A new and more practical thanheretofore way of eliminating erratic flow or plugging is by the use ofthe elongated probe valve geometry described elsewhere in precedingpatent application Ser. No. 08/096,919. However these methods are veryfrequently insufficient to prevent deposition of solid analyte upon themetering surfaces of the valve in the automatic restrictor. Thisdeposition produces flow fluctuations as the servo system, whichcontrols or self-adjusts the valve, grossly hunts around in an attemptto reset to the desired flow rate or pressure value. With difficultextractions the valve will plug entirely.

The preferred embodiment is a self-cleaning valve in which deposits donot get a chance to build up. It is surprising that this can be donewith reliability under the stringent pressure conditions forsupercritical extraction; pressures up to 10,000 psi. The problem isdifficult because self-cleaning metering or valving surfaces must be inmoving or scraping physical contact. Motional contact at pressuressufficient to shut off 10,000 psi fluid pressure results in galling ordestruction of the metering surfaces after an impractically shortlifetime. In an automatic restrictor these surfaces are in almostconstant relative motion as the valve automatically makes smalladjustments. In the restrictor valve of the preferred embodiment thesesmall adjustments are used to provide self-cleaning but almostparadoxically do not shorten the life of the valve.

From the above description, it can be understood that the variablerestrictor of this invention has several advantages, such as forexample: (1) it avoids loss of volatile analytes by dissolving thesample in a solvent; (2) the analytes are not deposited in therestrictor orifice, and thus flushing of the restrictor to maintainuniform flow and recover the analyte is not required; (3) the extractionconditions can be controlled with a controllable expansion devicedownstream from the extractor by modifying the pressure (density andsolvating power) of the supercritical fluid independently of flow rate;and (4) the necessity of secondary flushing of an associated connectingconduit to move the analytes from the restrictor system and convey themto the outside environment is eliminated.

DESCRIPTION OF THE DRAWINGS

The above noted and other features of the invention will be betterunderstood from the following detailed description when considered withreference to the accompanying drawings in which:

FIG. 1 is a schematic diagram illustrating the operation of a singlesupercritical fluid extraction system according to the invention;

FIG. 2 is a fragmentary sectional view of the extraction cartridge,breech plug pressure vessel and heating block;

FIG. 3 is a perspective view of another embodiment of the inventioncapable of automatic extraction of a series of samples;

FIG. 4 is a sectional view taken through lines 4--4 of FIG. 3;

FIG. 5 is a sectional view taken through lines 5--5 of FIG. 4;

FIG. 6 is a sectional view taken through lines 6--6 of FIG. 4;

FIG. 7 is a schematic drawing of a supercritical fluid extraction systemin accordance with an embodiment of the invention;

FIG. 8 is a fragmentary partly-schematic, partly-sectioned, broken awayview of variable restrictor assembly in accordance with an embodiment ofthe invention;

FIG. 9 is a partly broken away, partly sectioned view of a variablerestrictor forming a portion of the assembly of FIG. 8;

FIG. 10 is an enlarged fragmentary sectional view of the restrictor ofFIG. 9;

FIG. 11 is a a schematic view of electrical connections included in theassembly of FIG. 7 to control the temperature of the variablerestrictor;

FIG. 12 is a front elevational view, partly broken away and sectioned ofa variable restrictor used in the embodiment of FIG. 7;

FIG. 13 is a front elevational view, partly broken-away and sectioned ofanother embodiment of variable restrictor modified for automaticoperation in accordance with an embodiment of the invention;

FIG. 14 is a block diagram of a circuit usable in accordance with theembodiment of FIGS. 7 and 13;

FIGS. 15 and 16 are front and side elevational sectional views ofvariable restrictors in accordance with an embodiment of the invention;

FIG. 17 is a block diagram of another embodiment of circuit usable withthe embodiments of FIGS. 7, 13 and 15;

FIG. 18 is a block diagram of the circuitry for operating the system;

FIG. 19 is a schematic diagram illustrating another embodiment ofautomated supercritical fluid extraction;

FIG. 20 is a sectional view of one embodiment of extraction chamber,cartridge, breech plug, and flow splitter;

FIG. 21 is a sectional view of the chamber of FIG. 20 taken throughlines 21--21 in FIG. 20;

FIG. 22 is a sectional view of the vial septum piercing and solventcollection system assembly;

FIG. 23 is another sectional view of the piercing and solvent collectionsystem assembly taken through the vial heater and cooler;

FIG. 24 is a schematic circuit diagram of an interface and computercontrol system useful in measuring and controlling the temperature ofrestrictors in accordance with the embodiments of FIGS. 1-23 and 28-31;

FIG. 25 is a schematic circuit diagram of a circuit useful in sensingthe resistance and controlling the temperature of a restrictor inaccordance with previous embodiments;

FIG. 26 is a schematic circuit diagram of a circuit that computes theelectrical resistance of a restrictor for use in a temperature feedbackloop control system;

FIG. 27 is a schematic circuit diagram of the bridge circuit useful inthe control system for the temperature of a restrictor;

FIG. 28 is a partially broken away, partially sectioned front view of anautomatic variable restrictor having variable restrictor action throughaxial motion of a valve stem and self-cleaning action through rotarymotion of the valve stem;

FIG. 29 is an enlarged, fragmentary, partially sectioned view of theorifice region of the restrictor of FIG. 28;

FIG. 30 is a top view of the restrictor of FIG. 28; and

FIG. 31 is a partially sectioned, partially broken away side view of therestrictor of FIG. 28 with a solvent-trap collecting tube in place toillustrate action of the restrictor and a collection means.

DETAILED DESCRIPTION

In FIG. 1, there is shown a schematic fluidic diagram of one channel ofa dual-channel supercritical fluid extraction system 10 having a pumpingsystem 12, a valve system 14, a collector system 16 and a pressurevessel and fluid-extraction assembly 18. The pumping system 12communicates with two extraction cartridges within the pressure vesseland fluid-extraction assembly 18 and for this purpose is connectedthrough a tee joint 20 to two identical valve systems, one of which isshown at 14. Each valve system communicates with a different one of twoinlets for the corresponding one of two extraction cartridges.

The valve system 14 and a second valve system (not shown in FIG. 1)which is connected to the other branch of the tee joint 20 are eachconnected to two different collector systems 16, one of which is shownin FIG. 1, and to different ones of the two extraction cartridges in thepressure-vessel and fluid-extraction assembly 18 so that, two extractionoperations can be performed at the same time using the same pumpingsystem 12.

With this arrangement, the valve system 14 causes: (1) supercriticalfluid to flow from the pumping system 12 into a space between acartridge and the interior of the pressure vessel of the pressure-vesseland fluid-extraction assembly 18 for purging the outside of thecartridge and the inside of the pressure vessel; and (2) appliessupercritical fluid through the cartridge for extraction of a sample 134therein. Because the fluid is applied both to the interior of thecartridge and the exterior, the cartridge does not have to withstand ahigh pressure difference between its interior and exterior and can bemade economically.

In addition to controlling the flow of fluid into the pressure-vesseland fluid-extraction assembly 18, the valve system 14 controls the flowof: (1) purging supercritical fluid from the space between the cartridgeand interior of the vessel to the collector system 16 or to a vent; and(2) the extractant from the interior of the cartridge to the collectorsystem 16 for separate collection.

To hold sample 134 during an extraction process, the pressure-vessel andfluid-extraction assembly 18 includes a heating block 22, a pressurevessel 24 and a cartridge and plug assembly 26 with the cartridge andplug assembly 26 extending into the pressure vessel 24. The pressurevessel 24 fits within the heating block 22 for easy assembly anddisassembly. With this arrangement, the heating block 22 maintains thefluids within the pressure-vessel and fluid-extraction assembly 18 atsupercritical fluid temperature and pressure for proper extraction.

The cartridge and plug assembly 26 includes an extraction cartridgeassembly 30, a breech plug 32 and a knob 34 which are connected togetherso that: (1) the pressure vessel 24 is easily sealed with the breechplug 32; (2) the extraction cartridge assembly 30 snaps onto the breechplug 32 and the assembly may be carried by the knob 34; and (3) the knob34 serves as a handle to insert and fasten the assembly to the tubepressure vessel with the extraction tube communicating with an outletaligned with its axis and an inlet for the space between the internalwalls of the pressure vessel 24 and the exterior of the extractioncartridge 30 and for the interior of the extraction cartridge 30 beingprovided through a groove circumscribing the assembly inside thepressure vessel 24.

With this arrangement the extraction cartridge assembly 30 may be easilysealed in the pressure vessel 24 by threading the breech plug 32 into itand may be easily removed by unthreading the breech plug 32 and liftingthe knob 34. The extraction cartridge assembly 30 contains a hollowinterior, an inlet and an outlet so that a sample to be extracted may beplaced in the hollow interior and supercritical fluid passed through theinlet, the hollow interior and to the outlet to a collector. Theextraction cartridge assembly 30 serves as an extraction chamber ortube, the pressure vessel 24 serves as an extraction vessel and theheating block 22 serves as an oven as these terms are commonly used inthe prior art.

In the preferred embodiment, the knob 34 is of a low heat conductivitymaterial and it should include in all embodiments at least a heatinsulative thermal barrier located to reduce heating of the handleportion of the knob 34. It extends outside of the pressure vessel 24 andis adapted to aid in the sealing of the pressure vessel 24 and thebreech plug 32 together so that the extraction cartridge assembly 30 iswithin the pressure vessel 24 for maintaining it at the appropriatetemperature and the knob 34 is outside the pressure vessel 24 so as toremain cool enough to handle.

Although, in the preferred embodiment, the knob 34 is a heat insulativematerial, it only needs to be insulated against heat conducted from theinterior of the pressure vessel 24 and this may also be done by athermal barrier separating the pressure vessel 24 from the knob 34 suchas an insulative disc having a width of at least 1 millimeter andextending across the cross-section of the knob 34 to the extent of atleast 80 percent of the cross-section to effectively block anyconsiderable amount of transfer of heat between the cartridge and theknob 34. It should have a heat conductivity no greater than 0.05calories/cm. sec. degree C. at 30 degrees Centigrade.

The extraction cartridge assembly 30 has an opening which permits somesupercritical fluid to enter the pressure vessel 24 to follow one pathpassing into the extraction tube and out through an outlet of theextraction tube into a conduit leading to a collector. Othersupercritical fluid follows a second path around the outside of thecartridge to remove contaminants from the pressure vessel 24, equalizepressure and flow from another outlet. One of the inlet and outlet ofthe extraction cartridge assembly 30 enters along the central axis ofthe extraction cartridge assembly 30 and the other from the side topermit rotation of parts with respect to each other during seating ofthe pressure vessel 24 and yet permit communication of the extractioncartridge assembly 30 with the fluid source and with the collector. Toreduce wasted heat and fluid, the space between the outside of thecartridge and the inside walls of the pressure vessel 24 is only largeenough to accommodate the flow of purging fluid and to equalize pressurebetween the inside and outside of the cartridge. The volume between theoutside of the cartridge and the inside of the pressure vessel 24 isless than 10 cubic centimeters.

In the preferred embodiment, the inlet opens into an annular spacebetween the internal wall of the pressure vessel 24 and the cartridgeand plug assembly 26. The fluid follows two paths from the annularspace, both of which include an annular manifold with narrow holes and apassageway that communicates with the recess in the breech plug 32. Onepath opens into the extraction cartridge assembly 30. The other passesalong the narrow space outside the extraction cartridge assembly 30.Thus, supercritical fluid enters the extraction tube through alabrythian like path and at the same time passes outside the extractiontube so that the pressure inside the extraction tube is alwayssubstantially the same as that inside the pressure vessel 24. Becausethe pressures are substantially the same, the tube itself may be formedof relatively inexpensive plastics notwithstanding that a high pressureis desirable for extraction from the sample within the extraction tube.

The pressure vessel 24 is generally formed of strong material such asmetal and is shaped as a container with an open top, an inlet openingand two outlet openings. The inlet opening is sized to receive an inletfitting 42, the inlet fitting 42 being shown in FIG. 1 connected inseries with check valve 60A to corresponding heat exchanger 40. Each ofthe two outlet openings are sized to receive a different one of acorresponding purge valve fitting 44, and a corresponding extractantfluid fitting 46. With these fittings, the pressure vessel 24 is able toreceive the cartridge and plug assembly 26 in its open end and permitcommunication between the cartridge and the extractant fluid fittings,such as shown at 46. The inlet fittings, such as shown at 42, and purgevalve fitting, such as 44, permit communication with the inside of thepressure vessel 24.

To control the flow of fluids to and from the pressure vessel andfluid-extraction assembly 18, the valve system 14 includes an extractantvalve 50, a purge fluid valve 52 and an extracting fluid valve 54.

To introduce extracting fluid into the pressure-vessel andfluid-extraction assembly 18, the extracting fluid valve 54 communicateswith one branch of the tee joint 20 through tube 56 and with one end ofthe heat exchanger 40 through tube 58, the other end of the heatexchanger 40 communicating with the inlet fitting 42 through tube 60,check valve 60A and tube 60B. With these connections, the extractingfluid valve 54 controls the flow of fluid from the pumping system 12through the heat exchanger 40 and the pressure vessel 24 through theinlet fitting 42.

To remove purge fluid from the pressure vessel 24, the purge fluid valve52 communicates at one port with the purge valve fitting 44 through tube62 and with its other port through tube 64 (not shown in FIG. 1) withthe collector system 16 or with a vent (not shown) to remove fluidcontaining contaminants from the exterior of fluid extraction cartridgeassembly 30 and the interior of the pressure vessel 24.

To remove extractant from the extraction cartridge assembly 30, theextractant valve 50 communicates at one of its ports through tube 66with the extractant fluid fitting 46 and through its other port with thecollector system 16 through tube 68 for the collecting of the extractedmaterial, sometimes referred to as analyte or extractant, from thesample within the pressure vessel and fluid-extraction assembly 18.

For convenience, the valves 52 and 54 are mounted to be operated by asingle manual control knob 70. To supply fluid to the valve system 14:(1) the tube 56 carries pressurized fluid from the pumping system 12 totee joint 20; (2) tube 76 is connected to one arm of tee joint 20 tocarry pressurized fluid to another liquid extraction system unit notshown on FIG. 1; and (3) the remaining arm of the tee joint 20 isconnected through the tube 56 to an inlet fitting 74 of extracting fluidvalve 54. The valves 50, 52 and 54 are, in the preferred embodiment, SSitype 02-0120.

The extracting fluid valve 54 has a rotary control shaft 80 that isrotated to open and close its internal port. This shaft is operated byhand control knob 70 and carries spur gear 82 pinned to the controlshaft 80. Spur gear 84, which is pinned to control shaft 107 of purgefluid valve 52, meshes with spur gear 82 so that when control knob 70 isrotated clockwise, extracting fluid valve 54 is closed, but since thecontrol shaft 107 of purge fluid valve 52 is geared to turn in theopposite direction, the clockwise rotation of knob 70 opens purge fluidvalve 52.

The relative locations of the two gears on the two shafts are such that,in the first (clockwise) position of the knob 70, the extracting fluidvalve 54 is shut and the purge fluid valve 52 is open. Turning thecontrol knob 70 counterclockwise 130 degrees from this first positionopens extraction fluid valve 54 while allowing purge fluid valve 52 toremain open. Thus, both valves are open when the knob 70 is rotated 130degrees counterclockwise from the first position. When the knob 70 isrotated 260 degrees counterclockwise from the first position, extractionfluid valve 54 is open and purge fluid valve 52 is shut. Thus, there arethree definable positions for control knob 70: (1) clockwise with valve54 shut and valve 52 open; (2) mid position with both valves open; and(3) full counterclockwise with valve 54 open and valve 52 shut.

The extractant valve 50 includes an inlet fitting 120, outlet fitting122, manual control knob 132 and control shaft 126. The rotary controlshaft 126 is attached to control knob 132. When the extractant valve 50is opened by turning the control knob 132 counterclockwise from itsclosed position, fluid flows from the extraction cartridge assembly 30,through the extractant fluid fitting 46, the conduit 66, the valve inletfitting 120, the outlet fitting 122, through the tube 68 and into thecollector system 16.

The collector system 16 includes a purge coupling 90, a purge fluidcollector 92, an extractant coupling 94, an analyzing instrument 96, andan extractant fluid collector 98. The purge fluid flowing through thevalve 52, flows through purge coupling 90 into the capillary tube 110and from there into the purge fluid collector 92 where it flows into asolvent 100. Similarly, the extractant flowing through valve 50 flowsthrough tube 68 to the extractant coupling 94 and from there to thecapillary tube 128 and extractant fluid collector 98 which contains anappropriate solvent 104 in the preferred embodiment.

The analyzing instrument 96 may be coupled to the capillary tube 128through an optical coupling 102 in a manner known in the art. Theoptical coupling 102 is a photodetector and light source on oppositesides of a portion of the capillary tube 128, which portion has beenmodified to pass light. This instrument 96 monitors extractant and mayprovide an indication of its passing into the extractant fluid collector98 and information about its light absorbance. Other analyticalinstruments may also be used to identify or indicate othercharacteristics of the extractant.

In FIG. 2, there is shown a sectional view of the clipped-togetherextraction cartridge 26, knob 34 and breech plug 32 replaceablyinstalled in pressure vessel 24 which in turn has previously beenpermanently force fit into heating block 22. The pressure vessel 24 isfabricated of type 303 stainless steel for good machinability andcorrosion resistance and has within it a cylindrical central openingsized to receive the extraction cartridge 26, two openings for outletfittings in its bottom end, an opening in its cylindrical side wall toreceive an inlet fitting and an open top with internal threads sized toengage the external threads 188 of the breech plug 32. The heating block22 is fabricated from aluminum for good thermal conductivity andincludes a cylindrical opening sized to tightly receive the pressurevessel 24. The breech plug 32 and the extraction cartridge assembly 30are a slip fit within the pressure vessel 24. External threads 188 onbreech plug 32 engage in internal threads 200 within pressure vessel 24.

An annular self-acting high pressure seal 202 cooperates with a sealingsurface 186 to seal high pressure supercritical fluid from theatmosphere and an annular low pressure seal 204 spaced from the annularhigh pressure seal 202 prevents contaminated supercritical fluid in thespace between the interior of the pressure vessel 24 and the exterior ofthe extraction cartridge assembly 30 from getting back to thesupercritical fluid supply. These two annular seals 202 and 204 formbetween them a torroidal inlet chamber into which the outlet of thefluid inlet 42 extends to introduce fluid. Contamination may arise fromfingerprints or other foreign material on the outside wall of extractioncartridge assembly 30 and the low pressure seal 204 protects againstthis contamination. Seals 202 and 204 are Bal-Seal type 504MB-118-GFP.

Supercritical fluid is supplied to fluid inlet 42 and circulates in theannular space between high pressure seal 202 and low pressure seal 204,and then follows two paths into the pressure vessel 24 and extractioncartridge 30: one path for purging and one path for extraction. Anannular spacer 206 within the torroidal opening between seals 202 and204 has an hour-glass shaped cross section with radial holes through itand distributes incoming supercritical fluid from the inlet of fitting42 to the opposite side of the spacer 206 from which it flows topassageway 208 drilled in breech plug 32.

Because the passageway 208 extends radially from the recess 180 in thebreech plug 32 to the annular ring, it provides an open path for fluidbetween the two regardless of the orientation of passageway 208. Thepassageway 208 opens at an uncontrolled angular location with respect tothe inlet fixture 42 (inner side). Fluid flows from one side of theinwardly curved portion of the hour glass shaped spacer 206 thatcommunicates with the outlet of fitting 42 to the other side of theinwardly curved portion and from there to the passageway 208.

When the cartridge and plug assembly 26 are inserted into the pressurevessel 24 as shown in FIG. 2, the knob 34 is rotated and the externalthreads 188 of the breech plug 32 which form an eight thread per inchconnector engage internal threads 200 in the pressure vessel 24,screwing the breech plug 32 and attached cartridge and plug assembly 26down into the pressure vessel 24. When conical recess 210 in the bottomcap 144 reaches the external conical tip 212 of fitting adapter 214, thecartridge and plug assembly 26 is prevented from moving further down.

Screwing the breech plug 32 in further after the cartridge and plugassembly 26 has bottomed causes the upper flat annular surface offitting nipple 176 to bear upon the flat lower surface of a hat-shapedwasher 216. At this time, the hat-shaped washer 216 is residing againstthe upper surface of the head of a shoulder screw 218 which is threadedinto cylindrical hole 222 in breech plug 32.

Further screwing of the breech plug 32 into the pressure vessel 24causes the nipple 176 to lift the washer 216 off of the screw head andcompress a coil spring 201 between annular surface 205 and the ridge ofthe washer 216. Continued screwing of the breech plug 32 into thepressure vessel 24 causes annular flange 190 of breech plug 32 to bearupon the upper surface of the pressure vessel 24. This provides a limitstop with the coil spring 201 compressed, as shown in FIG. 2.

The force of the compression spring 201 is enough to provide a lowpressure seal between the hat-shaped washer 216 and the upper annularsurface 203 of the fitting nipple 176. More importantly, this force alsoprovides a low pressure seal on the mating concical surfaces of therecess 210 of lower cap 144 and the external conical tip 212 of thefitting adapter 214.

The sealing surface 186 acts as a pilot during the initial part ofinsertion to insure that the internal threads 188 do not getcross-threaded. A taper 189 at the end of the cylindrical sealingsurface 186 pilots the breech plug 32 past seals 202 and 204 so thatthey are not damaged during insertion of the breech plug 32.

The locations of recess 224, passageway 208, high pressure seal 202 andthe engaging threads 188 and 200 are chosen such that if the breech plug32 is inadvertently removed when the interior of the pressure vessel 24is pressurized, fluid within the pressure vessel 24 leaks past highpressure seal 202 and runs up the flights of the engaging screw threads188 and 200, and depressurizes the system while there is still adequatescrew engagement to ensure safety at the maximum rated operatingpressure. The maximum rated operating pressure of the embodiment shownin FIG. 2 is 10,000 psi. The maximum operating temperature is 150degrees Centigrade. The equipment need not be designed for operatingtemperatures above 300 degrees Centigrade and pressure above 30,000pounds per square inch.

After the breech plug 32 and the cartridge and plug assembly 26 areassembled into the pressure vessel 24 as described above, but before anextraction, the space between the cartridge and plug assembly 26 and thepressure vessel 24 is purged of contaminants. During such a purge orcleaning cycle supercritical fluid enters fluid inlet 42, is distributedby the annular spacer 206 and goes through passageway 208. It passesbetween the outer diameter of hat-shaped washer 216 and the insidecylindrical diameter 230 of the recess within breech plug 32. Fluid thencontinues down and passes the annular space between the outside diameterof engaging nipple 176 and inside diameter 230 of the recess 180 inbreech plug 32. The fluid passes garter spring 184 and circulates witheven circumferential distribution around the outside of top cap 148, theextraction tube 152, and the bottom cap 144. The flow is collected inthe annular space below the bottom cap 144 and above the bottom 240 ofpressure vessel 24 and exits through vent discharge fitting 44, carryingcontaminants with it.

Contaminated fluid between the exterior of extraction cartridge 26 andthe interior of high pressure vessel 24 does not make its way into theinterior of the extraction vessel. Low pressure seal 204 preventscontaminated fluid from reaching passageway 208. A labyrinth sealconsisting of the narrow gaps between the major diameter of fittingnipple 176 and the inside diameter 230 of recess 180, and between insidediameter 230 and the outside diameter of the hat-shaped washer 216,prevents contaminants from reaching the space above the hat-shapedwasher 216 by diffusion.

During a purge or cleaning cycle, there is downward flow ofsupercritical fluid through these gaps, and since the gaps are small,this downward fluid flow prevents eddies of contaminated fluid frompassing up through the gaps. These gaps are only a few thousandths of aninch. Because the top of nipple 176 and the conical recess 210 at thebottom of the extraction cartridge are sealed by spring pressure,contamination cannot enter in these ways.

For extraction, supercritical fluid entering fitting 42 is distributedin the space occupied by spacer ring 206, flows through passageway 208and flows down the few thousandths of an inch radial gap between theshoulder of shoulder screw 218 and the inside diameter of washer 216.The fluid continues to flow down and flows through passageway 250,porous frit 162 and into extraction volume 254 where it passes throughmaterial to be extracted. Extraction volume 254 is shown sized in FIG. 2for a 10 cubic centimeter volume to receive sample. After passing theextraction volume fluid, it is exhausted for sample collection throughfrit 160, passageway 260, fitting adapter 214 and out through fitting46.

All tubing, except tubing designated as capillary tubing, in thisdisclosure is 300 series stainless steel with an outside diameter of1/16 inch and inside diameter 0.02 inch.

In operation after assembly, the fluid flow associated directly with thepure fluid valve 54 (FIG. 1) exiting its port 114 (FIG. 1) flows throughtube 58 through the heat exchanger 40, which is formed by coiling acontiguous segment of tubing into a helix, through the check valve 60Aand through the tube 60B to the inlet fitting 42 of pressure vessel 24.The heat exchanger 40 actually resides in a longitudinal bore throughheating block 22 so that the heat exchanger is at the same temperatureas pressure vessel 24 and extraction tube 30. This preheats any fluidflowing into inlet fitting 42 to essentially the same temperature as theextraction cartridge assembly 30. This temperature is above the criticaltemperature for the fluid. Assuming that the pump 12 is set to produce aconstant fluid pressure greater than the critical pressure, fluidentering the pressure vessel 24 will be a supercritical fluid.

The check valve 60A prevents backflow of supercritical fluid out of thepressure vessel 24 and extraction cartridge 26 of a first channel of adual channel supercritical extraction system if there is a momentarydrop in pressure of the supercritical fluid at the location of the tee20. Such a pressure fluctuation could occur if the second channel of adual channel extraction system is suddenly purged while the firstchannel is extracting. Each channel requires such a check valve.

During a purge cycle, contaminated supercritical fluid leaves fitting44, flows through a tube 62 and enters the inlet fitting 116 of thepurge fluid valve 52. Then it exits the outlet fitting 118 and passesthrough the tube 64 to the coupling 90 (FIG. 1). The coupling 90 couplesthe quartz capillary tube 110 so that contaminated purge gas exitsthrough it. The bore of the capillary tube is small enough, such as 75micrometers, and its length long enough, on the order of a few inches,to provide enough fluid resistance to limit the flow to a convenientrate: for example 5 milliliters per minute with respect to displacementof pump 12, at a pressure of 3,000 psi. Pump 12 is a constant pressurepump so this fluid flow does not affect the pressure within pressurevessel 24 once the flow stabilizes.

The outer end of capillary 110 may be immersed a purge fluid collector92 (FIG. 1) containing an appropriate solvent 100 such as isopropylalcohol to serve as a collector. Bubbles through this solvent indicateproper flow and the solvent tends to prevent the end of the capillarytube 110 from being plugged by the exhausted contaminants. A solvent ischosen in a manner known in the art to dissolve contaminants so the endof the capillary tube 110 does not plug and so the solvent may later beanalyzed if desired to determine whether there was any contaminants onthe exterior of the extraction cartridge.

During an extraction cycle, extractant exits fitting 46 on pressurevessel 24 and passes through tube 66. This tubing extends to inletfitting 120 of extractant valve 50 which has rotary control shaft 126attached to control knob 132. When the extractant valve 50 is opened byturning it counterclockwise from its closed position, fluid exits fromits fitting 122, through tube 68 to fitting 94. Fitting 94 couples toquartz capillary tube 128.

Capillary tube 128 has a small enough bore, such as 50 micrometers, anda long enough length, on the order of several inches, to produce a flowrate, relative to the displacement of constant pressure pump 12, of aconveninent amount. For example, this may be two milliliters per minute.The end of the capillary tube 128 dips into solvent 104 in theextractant collector 98.

Isopropyl alcohol is under some circumstances used for solvent 104. Thissolvent 104 must be a good solvent for the extractant since it must trapthe extractant by dissolving it from the gas bubbling through it andmust prevent plugging at the end of the capillary tube 128.

The solvent 104 is removed after extraction and is analyzed to determinethe composition and amount of the extractant. Because of the pressureand temperature drop along the length of capillary 128 (and alsocapillary 110) fluid entering the capillary as a supercritical fluid (ora liquid if fitting 90 or fitting 94 is not heated) changes to a gas bythe time it reaches the far end where it dips into the solvent which isat room temperature.

Before using the extraction system 10, the pump 12 is set to the desiredpressure and the heater block 22 is set to the desired temperature. Thebottom cap 144 (FIG. 2) with the frit 160 is screwed onto the bottom ofextraction tube 152. The internal cavity 158 is then filled or partlyfilled with sample to be extracted. The frit 162 and top cap 174 arethen screwed on to the top of extraction tube 152 forming the cartridgeand plug assembly 26. The cartridge and plug assembly 26 is then clippedinto breech plug 32 by shoving the fitting nipple 176 on the extractioncartridge past garter spring 184 located within breech plug 32. Knob 70is set to the vent position closing valve 54 and opening valve 52 (FIG.1). Valve 124 is set to the clockwise closed position.

The assembled breech plug and extraction cartridge are inserted intopreheated pressure vessel 22 and manually screwed with knob 34 intopressure vessel 24 until annular flange 190 contacts the top of pressurevessel 24 (FIG. 2). The pressure vessel has been preheated under controlof a thermocouple temperature controller to the desired temperature. Thecartridge and plug assembly 26 within pressure vessel 24 rapidly risesto the required temperature.

After insertion of the cartridge and plug assembly 26 into the sampleblock 24, valve knob 70 is rotated to the purge position. In thisposition, both valves 54 and 52 are open. Since the pump 12 has alreadybeen set to the desired fluid pressure, fluid flows through tubes 76,56, valve 54, tube 58, heat exchanger 40, tube 60, check valves 60A and60B and inlet fitting 42 into the cavity 180. Since valve 124 is closed,supercritical fluid preheated to the correct temperature by heatexchanger 40, flows past hat-shaped washer 216, fitting nipple 176 andaround the outside of cartridge and plug assembly 26. This supercriticalfluid dissolves any contaminants on the outside of extraction cartridgeassembly 30 and any contaminants inside pressure vessel 24. The hotsupercritical fluid also insures that the extraction cartridge assembly30 is at the proper operating temperature. The supercritical fluidflushes the contaminants from fitting 44, through tube 62, valve 52,tube 64, the fitting 90 and the capillary tube 110.

After a short purge cycle, control knob 70 is set to the extractposition. This sets valves 54 and 52 so that valve 54 is open and valve52 is closed. Immediately after making this setting, the operator opensvalve 124 by rotating knob 132 counterclockwise in the extractdirection. Pressurized fluid flows through valve 54 into heat exchanger40 so that it is at the desired supercritical temperature, and flowsinto fitting 42. It then flows into cavity 180 and past the annularspace between shoulder screw 218 and the inside diameter of hat-shapedwasher 216, after which it passes through the interior of fitting nipple176, through passageway 250 and into the extraction vessel 26. Thissupercritical fluid flowing through the interior sample cavity 254 ofthe extraction cartridge extracts analyte from the sample 134 containedwithin the cavity 254.

Supercritical fluid with the analyte in solution passes out through thefitting 46, the tube 66, the valve 124, the tube 68, the coupling 94 andthe capillary tube 128 which leads into the collecting solvent 104within test tube 98. The analyte is dissolved in the solvent 104 forlater analysis. When the extraction is complete, knob 132 is rotatedclockwise in the closed direction, closing valve 124. This stops theflow of supercritical fluid into the extraction cartridge 26. Knob 70 isthen rotated clockwise to the vent position. This closes valve 54 andopens valve 52, depressurizing the pressure vessel 24 and cartridge andplug assembly 26 through capillary tube 110.

When bubbles stop issuing through the end of capillary tube 110,depressurization is complete. Knob 34 is rotated counterclockwise tounscrew the breech plug 32 and the attached cartridge and plug assembly26 from pressure vessel 24. Extraction cartridge assembly 30 may now beopen to empty spent sample.

In FIG. 3, there is shown a simplified perspective view of anotherembodiment 10A of supercritical fluid extraction system having a cabinet400 containing a drive section in its lower portion (not shown in FIG.3), an extraction section in the upper portion of the cabinet (not shownin FIG. 3), a sample injection section 406 and a fraction collectionsection 408. The supercritical liquid extraction system 10A iscontrolled from a panel 410 on the front of the cabinet 400 and thedrive section operates the extraction section, the sample injectionsection 406, and the fraction collection section 408, which cooperatetogether to extract a plurality of samples sequentially and collect theextractant from the samples in separate containers with minimumintervention by an operator.

The supercritical fluid extraction system in the embodiment 10A operatesin a manner similar to that of the embodiment of FIG. 1 but is adaptedto cooperate with the novel sample injector and fraction collector. Withthis arrangement, a series of samples to be extracted are preloaded intoa means for holding the samples and the samples are automaticallyinjected one at a time into the extractor. In the extractor,supercritical fluid is supplied to the samples and an extractant isremoved from the samples one by one. To aid in correlating theembodiment 10 (FIG. 2) and the embodiment 10A (FIG. 3), similar partshave the same reference numerals but in the embodiment of FIGS. 3, 4, 5and 6, the numerals include the suffix "A".

The extractant is supplied to individual containers or individualcompartments of one container in a fraction collector. Thus, a pluralityof extractions are performed on a plurality of different preloadedsamples without the need for manually loading samples or initiating theflow of the supercritical fluid for each individual sample. The samplesare automatically mechanically moved one by one into the extractor forextraction instead of being individually physically injected by anoperator.

The cabinet 400 has a lower portion 412 generally shaped as a rightregular parallelopiped with an angled control panel 410 and upstandingupper portion 414 which is another right regular parallelopipedextending upwardly to create a profile substantially shaped as an "L"having a common back portion or rear panel 416 which may contain fansand connections for supplementary pumps and the like. A fluid fitting420 extends from one side to permit liquid or near supercritical fluidsto be introduced into the cabinet 400. The L-profiled cabinet 400 has anangled front panel 410 for convenient use of controls and a top surfaceon the foot of the "L" for manipulation of samples to be injected andextractants that are collected.

To permit access to the interior of the cabinet 400, the upper portion414 includes a hinged front access panel 422 having hinges 426 at itstop so that it can be pivoted upwardly. It includes an opening 424 nearits bottom to permit the entrance of fraction collector receptacles thatare relatively tall. It extends downwardly to a point spaced from thetop surface of the lower portion 412 of the cabinet 400 a sufficientdistance to permit the entrance of normal receptacles used in the sampleinjector and the fraction collector.

The sample injection section 406 includes a sample reel 430 which isformed of upper and lower rotatable plates 432 and 434 spaced verticallyfrom each other and containing holes in the upper plate 432 and openingsin the lower plate 434 which receive cylindrical tubular sleeves 436having vertical longitudinal axes and open ends. The upper open end 438permits samples to be received and to be removed as the sample reel 430is rotated into the extractor.

With this arrangement, the sample reel 430 may be rotated to movesamples one by one into the extractor for processing. The sample reel430 is horizontal and extends into the upper portion 414 of the cabinet400 and into the extractor assembly with its vertical center of rotationbeing outside of the upper portion 414 to permit ready access to anumber of the sleeves 436 by users and yet to permit sequential rotationby automatic means into the extractor. In the preferred embodiment,there are 24 sleeves for containing 24 distinctly different sampleswhich can, without human intervention, be moved into the extractor.

To receive extractant, the fraction collection section 408 includes ahorizontal fraction collector reel 440 mounted concentrically with thesample reel 430 but having a smaller diameter to be inside the samplereel 430 having a plurality of openings 442 circularly arranged inspaced apart relationship with each other about the periphery of a topplate 446 of the fraction collector reel 440 and having in its center aknob 444 by which the fraction collector reel 440 may be lifted andremoved from the cabinet 400. With this arrangement, the fractioncollector reel 440 may be lifted and removed or reinserted after thehinged access panel 422 is pivoted upwardly about the hinges 426.

When the fraction collector reel 440 is in place, it is rotatedautomatically through the opening 424 into a location in which one ormore individual containers 442 may receive extractant. The fractioncollector reel 440 is moved alternately with the sample reel 430 andindependently of it so that, after a sample injection and extraction,one or more of the openings 442 are moved into position to receive theextractant prior to the injection of another sample for extraction.

Because the reels 430 and 440 rotate within the upper portion 414 of thecabinet 400 with a portion of its periphery outside of the cabinet 400,the collected extractant may be removed and new sample added duringoperation of the equipment. For this purpose, the receptacles for thefractions and the receptacles for the samples have upward open ends andare mounted with their axes vertical.

In FIG. 4, there is shown a longitudinal sectional view through lines4--4 of FIG. 3 showing the cabinet 400, the drive section 402 within thecabinet 400, the extraction section 404, the sample injection section406 and the fraction collection section 408. The drive section 402includes a control system 450, a sample-and-extractant container reeldrive assembly 452, a sample injector drive 454 and a fluid drive orpump 456. The control system 450 receives information from the controlpanel 410 and conveys information to it through a cable 458. It alsocontrols the pump 456, the sample-and-extractant trap container reeldrive assembly 452 and the sample injector drive 454, which cooperatetogether to move samples into position, inject them into the extractor,pump fluids through the extractor to extract the samples and collect thesamples in sequence one by one.

To inject samples into the extraction section 404, the sample injectionsection 406 includes the sample-and-extractant container reel driveassembly 452, the sample reel assembly 430, and a cartridge injectorassembly 460. The sample-and-extractant container reel drive assembly452 drives the sample reel assembly 430 to carry a cartridge assembly30A onto the cartridge injector assembly 460 which lifts it under thecontrol of the sample injector drive 454 upwardly into a pressure vessel24A for the purpose of extracting a sample within the cartridge assembly30A. The cartridge assembly 30A and the pressure vessel 24A are similarto the cartridge assembly 30 and pressure vessel 24 of the embodiment ofFIGS. 1 and 2 and are only adapted such as by having their top andbottom sides reversed to permit the cartridge assembly 30A to beinserted from the bottom into the pressure vessel 24A and be more easilysealed therein for extraction and removed by gravity after extraction.

To drive the sample reel assembly 430, the sample-and-extractantcontainer reel drive assembly 452 includes a central transmission andmotors on each side that drive the transmission under the control of thecontrol system 450 to drive either one or both the sample injector reelassembly 430 and the fraction collector reel 440.

The sample injector reel assembly 430 includes the top plate 432, thebottom plate 434, both of which are rotatable together to carry aplurality of sleeves 436 sequentially, one at a time, into position forthe repeated injecting of cartridges one by one into the pressure vessel24A and the removal of the cartridges from the pressure vessel 24A andthe return of them to the reel assembly 430 one by one so that only onecartridge is in the pressure vessel 24A at a time.

Within the extraction section 404, a stationary bottom plate 462 has ahole 464, with the hole being aligned with the open-bottom end of thepressure vessel 24A and the upper end of the cartridge injector assembly460. Consequently, the cartridge assemblies such as 30A are rotated oneby one above the open end 464 in the bottom plate 462 for movementupwardly into the pressure vessel assembly 24A by the cartridge injectorassembly 460 under the control of the sample injector drive 454 forextraction of the sample therein. With this arrangement, a stationaryplate 462 holds the cartridge assemblies 30A in place as they arerotated by the upper and lower plates 432 and 434 until they aresequentially brought over the opening 464 through the stationary plate462 for elevation into the pressure vessel 24A.

To inject cartridges into the pressure vessel 24A, the cartridgeinjector assembly 460 includes the sample injector drive 454, a pinion470, a gear 472, a multi-threaded, fast action nut 474, a correspondingscrew 476, and piston or plug 32A. The pinion 470 is mounted to theoutput shaft of the drive gear motor 454 and engages the teeth of gear472. The gear 472 is fastened to or integrally formed with the drive nut474 which, as it rotates, moves the screw 476 upwardly or downwardly.The support platform 475, piston or plug 32A and sample container 30Aare carried by the top of the screw 476 and are moved upwardly anddownwardly. The top surface of the plug 32A, which is supported by thescrew 476 in its lower position is flush with the bottom of the opening464 in the fixed plate 462 to support a cartridge such as 30A thereinand in its top position positions the piston or plug 32A at the bottomof the pressure vessel 24A. Plug 32A carries self-actuated,spring-biased, cylinder seals, such as those made by the Bal-SealCorporation. These seals provide a high pressure fluid-tight sealbetween the plug 32A and the inner wall of the pressure vessel 24A.

With this arrangement, the piston or plug 32A is sealable against thewalls of the pressure vessel 24A during the extraction process aftermoving the cartridge assembly 30A upwardly into the pressure vessel 24A,and after extraction, can move the cartridge assembly 30A downwardlyback to the sample reel assembly 430 for rotation out of the upperinjector housing 414 as a new cartridge is moved into position forinjecting into the pressure vessel 24A. A bearing mount rotatablysupports the nut 474 while maintaining it in the same vertical positionso as to move the rapid-advance screw or other screw 476 upwardly anddownwardly.

The plug 32A serves a function similar to the breech plug 32 in theembodiment of FIGS. 1-2 and contains within it an opening supporting aspring 201A and a support block 482 so that the support block 482 isbiased inwardly against the cartridge end 148A to move the cartridge 30Ainto place against fittings for supercritical fluid.

To extract the sample in the cartridge 30A after it has been moved intoposition and the breech plug 32A fastened in place for a seal,extracting fluid is applied through the fitting 42A in a manner similarto the embodiment of FIG. 1, so that the extracting fluid flows throughone path into the cartridge 30A and through another path over theoutside of the cartridge 30A into the fitting 44A and from there to apurge collector or vent. The extractant, after passing through thecartridge and the sample, exits from a fitting 46A and proceeds to thesample collector in a manner to be described hereinafter.

To pump fluid such as carbon dioxide into the pressure vessel 24A at atemperature proper for supercritical extraction: (1) the pump 456includes a pump head 490 and an electrical motor 492; and (2) thepressure vessel 24A has an aluminum heating block 22A over it, anopening 278A in the aluminum heating block, a rod-shaped heating element274A in the aperture 278A, the extracting fluid fitting 42A and a heatexchanger 40A entering the aluminum heating block 22A at aperture 270A.The motor 492 drives the pump mechanism 490 to pump fluid into theaperture 270A, through the heat exchanger 40A within the aperture 270A,through the connecting tubing 60A and the fitting 42A and into thecartridge 30A and the pressure vessel 24A. The aluminum block 22Acontrols the temperature of the fluid, which may be carbon dioxide orany other useful extracting fluid to keep it above the supercriticaltemperature for that fluid, and for that purpose, the heating rod 274Awithin the aperature 278A is used when necessary to heat the aluminumblock 22A.

The pump 456 may be any suitable pump, but one appropriate pump forcarbon dioxide is the pump used in the Isco model 2350 HPLC PumpingSystem sold by Isco, Inc., Lincoln, Nebr. However, for best results whenusing carbon dioxide, the stroke of this pump is modified from tenmillimeters to fifteen millimeters, and smaller, lower trapped-volumecheck valves are used. These modifications increase the compressionratio of the pump from 1.7:1 to 2.6:1 and increase the displacement by amultiple of 1.5. An additional change is to use Carpenter Technologies182FM stainless steel in the pump head, instead of type 316, for betterthermal conducting. The pumphead and inlet line to the pump arepreferably thermoelectrically cooled.

To collect extractants, the fraction collector section 408 includes thefraction collection reel 440, the sample-and-extractant container reeldrive assembly 452, a purge fluid outlet system 520 and an extractantfluid outlet system 522. The fraction collection reel 440 movesreceptacles such as 98A into position within the housing 414 where theextractant fluid outlet system, 522 to be described in greater detailhereinafter, causes fluid from the fitting 46A in the pressure vessel24A to flow outwardly and into the receptacle 98A after piercing a sealtherein. The purge fluid system 520 causes purge fluid to flow from thepurge fluid fitting 44A to a pressure control unit and finally to anexhaust or collection unit.

To move the collection receptacles 98A into position, the fractioncollection reel 440 includes a knob 444, an intermediate plate 448, anupper plate 446, a lower disk plate 530 and a drive rod 532. The driverod 532 rotates within the fixed disk 530 and carries above them theupper and lower plates 446 and 448. The upper and lower plates 446 and448 have aligned circumferentially spaced holes through them, each ofwhich can receive a collection vial such as 98A. The lower disk 530 doesnot have holes and supports the plates as they are moved. The knob 444may be used to lift the fraction collector reel 440 from the center ofthe sample injector reel 430 after the hinged front access panel 422 hasbeen opened about its hinge 426.

The sample-and-extractant container reel drive assembly 452 moves thecollection vials one by one inside the upper portion of the housing 414to receive extractant. One or more such vessels 98A may be moved inplace each time a sample cartridge 30A is extracted so that thereceptacles 98A are moved alternatively with the sample cartridges 30A,although several receptacles 98A may be moved in the time between movingone of the sample cartridges 30A into a pressure vessel 24A and the timethe sample cartridge is removed from the pressure vessel 24A. Theextractant passes through fitting 46A and into the fraction collectorreceptacles 98A in a manner to be described hereinafter.

The purge fitting 44A communicates with the extraction volume in thecartridge 30A and is connected to a Tee-joint tube 542 through tubing62A. A second arm of the Tee-joint tube 542 is connected to anover-pressure safety diaphram 540 calibrated to burst at 15,000 poundsper square inch. This is an excess of the maximum rated working pressureof 10,000 pounds per square inch for pressure vessel 24A. The remainingarm of the Tee-joint tube 542 is connected to the purge valve 52A. Theother side of the purge valve 52A is connected to the first side of asecond Tee-joint tube 544 through the tube 64A. The second side of theTee-joint tube 544 is connected to an exterior vent port 546 through atube 548. The third arm of the Tee-joint tube 544 is connected to theexhaust tube 110A which vents the fraction collection vial 98A. Withthis arrangement, the purge fluid flowing through fitting 44A is removedand a tube connected to the vent port 546 is also used to vent thesample receptacle 98A in a manner to be described hereinafter.

In FIG. 5, there is shown a simplified sectional elevational view of theembodiment 10A of supercritical fluid extractor taken through lines 5--5of FIG. 4 having the sample-and-extractant container reel drive assembly452, the pump 456 and the extractant fluid outlet system 522. Thesample-and-extractant container reel drive assembly 452 may selectivelymove either the sample reel 430 or the fraction collection reel 440under the control of the controller 450 (FIG. 4).

To selectively drive the fraction collection reel 440, thesample-and-extractant container reel drive assembly 452 includes afraction collection spindle 532, a tubular shaft 580, a bevel gear 582,a bevel gear 584 and a gear motor 586. The controller 450 controls thegear motor 586 to rotate the fraction collection reel 440. For thispurpose, the spindle 532 is held by the tubular shaft 580. The bevelgear 582 is fastened at the end of the spindle 532 and meshes with thebevel gear 584 on gear motor 586. The controller 450 moves these gearsinto meshing position and causes the motor 586 to rotate its outputshaft so as to drive the collection reel 440 (FIGS. 3 and 4) and not thesample injector reel 430.

To move the sample injector reel 430, the sample-and-extractantcontainer reel drive assembly 452 includes the tubular shaft 580supported by bearing block 590, fraction collection spindle 532, bevelgear 588, bevel gear 592 and gear motor 594. The controller 450 actuatesgear motor 594 to cause the bevel gear 592 to rotate. The bevel gear 592meshes with the bevel gear 588 which is attached to the bottom end ofthe fraction collection spindle 532.

To cause extractant to flow into the fraction collection vial 98A, theextractant fluid outlet system 522 includes a gear motor 552, a pinion554, a gear 556, a lead screw 558, an arm 560, and a restrictor tube66A. The vials 98A have a seal 550 over the top, which seal can bepierced.

To cause the seal 550 to be pierced and extractant to flow into the vial98A, the controller 450 starts the gear motor 552 which rotates itspinion 554 which is in engagement with the gear 556. The pinion 554rotates the gear 556, which engages and is fastened to the rotating leadscrew 558. The arm 560 is mounted for movement by the lead screw 558 andlowers it into a position where the restrictor tube 66A pierces the cap550 on the collection vial 98A and moves its tip below the surface 564of the collection fluid within the vial 98A. As the extractant flowsinto the tube, exhaust is removed from the tube through an exhaust tube110A (FIG. 4 in addition to FIG. 5).

If either the tube 66A or the tube 110A are stiff or otherwiseinconvenient to bend, it is advantageous to raise the collecting vial98A up to tubes 66A and 110A, instead of lowering the tubes into thecollecting vial. This alternate arrangement does not pose any difficultyas the collecting vial 98A may be raised by a support similar to plug32A, which support is connected directly to plug 32A so that it moveseither synchronously or independently with plug 32A.

With either arrangement, extractant flows through the fitting 46A (FIG.4) from the sample cartridge 30A (FIG. 4) through the tubing 522 (FIG.4), the valve 50A and the restrictor tube 66A. Extractant residing inbubbles from the tube are captured through trapping fluid 104A wherebyextractant is trapped in the trapping fluid 104 in the vial 98A andextracting fluid passes out through the exhaust tube 110A, Tee-jointtube 544 (FIG. 4), tube 66A and exhaust port 546 (FIG. 4). Aftercollection of the extractant, the motor 552 moves in the reversedirection and raises arm 560 which removes the restrictor tube 66A andexhaust tube 110A from the vial 98A.

Because the pump head 490 is heated by pumping at high compression, boththe pump head 490 and incoming fluid line are preferably cooled. In thepreferred embodiment, they are cooled thermoelectrically (Peltiereffect). The pump head 490, the inlet check valve housing 494 are formedof carpenter 182FM stainless steel rather than type 316 stainless steelto increase their thermal conductivity.

In pumping, the pump drive motor 492 (FIG. 4) drives a cam within camhousing 495 through appropriate gear train within the gear housing 496.The rotating cam within the cam housing 495 operates a pump plungerwhich cooperates with the pump head 490 (FIG. 5) to draw liquid carbondioxide through inlet check valve assembly 494 and discharge it throughoutlet check valve assembly 436. In one embodiment, the Peltier coolingplate 500 is mounted to the flat face of the pump head 490 (FIG. 5) withcooling fins 502 mounted for good thermal contact to the opposite sideof the Peltier cooling plate 500.

When an electric current is passed in the proper direction through thePeltier cooling plate 500, heat is withdrawn from the pump head 490(FIG. 5) and rejected into the cooling fins 502. A fan 504 driven by anelectric motor 493 (FIG. 4) withdraws heat from the fins 502. AnotherPeltier-effect cooled heat exchanger is also utilized in the inlet line.

To control the speed of the motor 492 (FIG. 4), a tachometer wheel 505is mounted to the shaft of motor 492 (FIG. 4) with a photoelectrictachometer sensor 510 mounted to provide signals reading indicia on thewheel. The signals from the photoelectric tachometer 510 indicate thespeed of motor 492 and thus the pumping speed of pump 456. These signalsare compared in the controller 450 and utilized to control the speed ofthe motor 492.

To control the pressure on the outlet line 512 from the pump, a pressuretransducer 514 (FIG. 6) generates a signal indicating the pressure. Thissignal is used as a feedback signal to control the pumping speed. Thisstructure is provided by existing pumps such as the Isco model 260Dpump.

In FIG. 6, there is shown a sectional view, partly simplified, takenthrough lines 6--6 of FIG. 4 having a locking mechanism 614 for lockingplug 32A into the pressure vessel 24A and a control mechanism 616 forcontrolling the extraction fluid. As best shown in this view, thelocking mechanism 614 includes a gear motor 600, a pinion 602, a rack604, a locking pin 606, a hole 609 in the pressure vessel 24A and a hole610 in the piston or end piece or breach plug 32A and a hole 612 throughthe other side of the pressure vessel 24A. Instead of a pin 606, a yokeof the type conventionally used as a Winchester 94 rifle lockingmechanism advantageously may be used. This type of locking mechanism isa yoke mounted to a pinion 602 and rack 604 as shown in FIG. 6. In thismechanism, a plate with a slot cut out of it to form a yoke is moved bythe rack and pinion to pass under the plug 32A to hold it againstpressure and provide strong support therewith by further engaging slotsin the pressure vessel 24A. The aforementioned slot in the plateprovides clearance for the screw 476.

In operation, the gear motor 600 is caused by the control system 450(FIG. 4) to drive locking pin 606 through the opening 609 in thepressure vessel 24A, through the opening 610 in the piston 32A andthrough the opening 612 in the pressure vessel 24A by rotating thepinion 602 to drive the rack 604 that carries the locking pin 606, thuslocking the cartridge 30A (FIG. 4) in place within the pressure vessel24A.

To control the flow of extracting fluid from the pump 12 (FIG. 1) intothe pressure vessel 24A and cartridge 30A, the control mechanism forextracting fluid includes the gear motor 570 and valve 54A that isconnected at one end to the conduit 58A that extends from line 512 andpressure transducer 514 to the conduit 58 which passes into the heatexchanger 40 (FIG. 1). In operation, the gear motor 570 under thecontrol of the control system 450 opens the valve 54A to permit the flowof extracting fluid into the cartridge 30A and pressure vessel 24Aduring an extraction operation. It also rotates in the oppositedirection after extraction is complete to close the valve 54A.

The sample cartridge 30A (FIG. 4) is composed of a tubular sleeve orbody portion 140A (FIG. 4) and end pieces 144A (FIG. 4) and 148A (FIG.4). The end pieces 144A and 464A are made of stainless steel,hard-coated aluminum or an inert plastic and carry a stainless steelfrit or filter disk centered in the interior of each. The flat, narrowedends of the tubular sleeve 140A seal against PTFE washers around thefrits which seal against the end pieces at the location between thediameters of the filter disks and the inside diameters of the end pieces144A or 148A respectively.

In FIG. 7, there is shown a supercritical fluid extraction system 10having a pumping system 12, a supercritical fluid extractor 13, apressure transducer 15, a variable restrictor system 11 and collectionsystem 19. The pumping system 12 pumps supercritical fluid through thefluid extractor 13 where it dissolves sample. The sample andsupercritical fluid then flows from the fluid extractor 13 through theconduit 31 where it influences tha pressure transducer 15 to indicatepressure on electrical conductors 47 and to the variable flowrestriction system 11 into the collection system 19.

During this process, the variable restriction system 11 modifies thepressure of the supercritical fluid in such a way as to control thedensity and solvating power of the fluid and permits abrupt expansion ofthe supercritical fluid to control where the analytes come out ofsolution. The expansion of the supercritical fluid is controlled toavoid the requirement for flushing of a restrictor and associatedconnecting conduit to remove the sample from them.

To pump supercritical fluid, the pumping system 12 includes a pump 23and a pump controller 25 connected to the extractor 13 through thetubing 27. Clean, supercritical extraction grade CO₂ enters aconventional syringe pump 23 and is pressurized to supercriticalpressures. A suitable pump controller 25, monitors and controls thepressure developed in the pump. The controller 25 and pump provide formeasurement of fluid pressure and fluid flow rate. The controller alsoprovides a pressure set point and pressure controller for constantpressure operation and a flow set point and flow controller for constantflow operation.

A suitable syringe pump may be an Isco Model 260D Syringe Pump and asuitable controller may be an Isco "D" Series Syringe Pump Controller.Both are available from Isco Inc., 4700 Superior, Lincoln, Nebr. 68504U.S.A. The supercritical fluid is transferred to an extractor. Suitableextractors are disclosed in U.S. Pat. No. 5,094,753 and are availablefrom the aforementioned Isco, Inc., under the designation ISCO Model SFX2-10 Supercritical Fluid Extractor. The fluid is heated within theextractor to supercritical temperatures while maintaining supercriticalpressure.

The analytical sample is within an extraction chamber inside theextractor 13 under plug 29, and the supercritical fluid extracts theanalytes from the sample. The extraction chamber has a fluid inlet forextraction fluid to extract the sample and an outlet for fluid withextracted analyte in solution.

To receive the analyte, the collection system 19 includes a tube 34, anorifice tip 39 at the end of the tube 34, a collection vessel 37,collection solvent 35 within the collection vessel 37, a pierceableseptum 41 and a vent tube 43. The supercritical fluid with dissolvedanalytes flows from the outlet of the extractor through tubing 31 topressure transducer 15 and then to the variable restriction system 11through transfer tubing 33. If the transfer tubing 31, transducer 15,tubing 33 and restrictor 11 are not heated, the supercritical fluid maycool to a liquid before reaching the orifice tip 39. This is often of noconsequence as the liquid may satisfactorily solvate the analyte and theorifice tip serves to depressurize either supercritical fluid or liquid.

The orifice tip 39 of the variable restriction system is immersed in thecollection solvent 35 in a collection container 37. The rate at whichthe supercritical fluid is discharged into the collection fluid is setby control knob 17 on the variable restriction system 11. At thedischarge orifice 39 of the variable restriction system 11, thesupercritical fluid or liquid expands into a gas and bubbles through thecollection solvent 35, depositing the extracted analyte in thecollection solvent.

To insure that as much as possible of the analyte is deposited in thecollection solvent 35 or collection container, the supercriticalpressure conditions are maintained all of the way down to the orificetip 39. The collecting tube has a pierceable septum 41 covering itsmouth. The septum is pierced by the probe of variable restrictor 11 andby vent tube 43. The vent tube may be led to a fume hood (not shown) incase the gas issuing from it is toxic or flammable. Conductors 47receive pressure representing electrical signals from the transducer,which signals are used to control pressure as explained hereinafter.

In FIG. 8, there is shown a partly-schematic, partly-sectioned view of amanually-controlled variable-valve restrictor assembly 11 having a valveadjustment section 1013, a temperature control section 1015 and a needlevalve section 1011. The needle valve section 1011 is: (1) adjusted as toorifice opening size by the valve adjustment section 1013 to which it isconnected to control the pressure in the pressure chamber or column bycontrolling the release of fluid; and (2) is positioned to provide theeffluent directly into a collection chamber environment to avoid loss ofsample and the use of time in removing sample from tubing. Thetemperature control section 1015 controls the temperature of theeffluent at the orifice to avoid undesired cooling.

As shown in FIG. 8, the restrictor valve is of the needle valve type andthe needle valve section includes a metering restriction orifice orexpansion area 1248, a control needle 1256, a control needle tip 1257, abarrel tube 1234, a barrel tube tip 1233, a fluid-passing orifice 1240and a fluid connection hole 1287. The control needle 1256 cooperateswith the hole 1287 to carry the flow of effluent into the needle valvewhere it is received in a space between the barrel tube 1234 and controlneedle 1256 that leads to the expansion area 1248. At the expansion area1248, the barrel tube tip 1233 and control needle tip 1257 cooperate tocontrol the expansion and release of the effluent through thefluid-passing orifice 1240 directly into the collection environment.

To permit fluid flow to the clearance area, there are a connectingannular clearance between control needle 1256 and hole 1287 and anannular clearance between the inside diameter of barrel tube 1234 andthe coaxial needle 1256. These provide clearance for fluid flow from thefitting 1282 down to the metering, restriction, or expansion area 1248of the valve where the pressure drop takes place. For this purpose, thecontrol needle tip 1257 rotates and reciprocates within the barrel tube1233 varying the size of the fluid-passing orifice at expansion area1248. The point angle of the needle tip 1257 is more acute than that ofthe female seat in the barrel tip 1233, making the narrowest portion ofthe orifice at the far distal surface of the tip at 1240.

The expansion of the supercritical fluid occurs essentially at thedischarge opening 1240 of the tip 1233, 1257, making the extent ofconduit exposed to expanded extraction fluid almost without length, sothe expansion occurs in contact with the collection solvent, and theanalyte precipitates from the extraction fluid directly into thecollection solvent or other collecting trap. This improves collectionefficiency and decreases plugging at the orifice.

Supercritical pressure is maintained down to the orifice or restrictionregion 1240 of the distal end of the barrel tip, which is inserted intothe midst of a collection solvent or other collection trap. The distancebetween point of the needle tip 1257 and the recessed seat in the barreltip forms a variable orifice at 1240 which controls the flow rate.

To adjust the pressure and flow rate at the variable orifice 1240, theadjustment section 1013 includes an adjustment knob 1266, a controlneedle head 1265, male and female screw threads 1264, and an actuationnut 1268. The needle is adjusted using knob 1266 which is fastened tothe control needle head 1265 for rotation therewith. The upper end ofthe needle 1256 is silver soldered into a recess in the underside ofcontrol needle head 1265 for rotation and reciprocation with the controlneedle head and adjustment knob 1266 and head 1256 within the controlactuation nut 1268. The control actuation nut includes internal threadsthat cooperate with the external threads on the control needle head.

With this arrangement, rotating the knob 1266 threads the needle head1265 and needle 1256 up and down through female threads in the actuationnut 1268. The resulting vertical motion causes the space between the endof the needle tip and the end of the barrel tip to vary, developing avariable orifice 1240. Expanded fluid is then discharged directly intothe collection fluid or into the collection vessel. In this design, theentire needle and knob assembly (1257 through 1266) rotates with respectto the barrel tip 1233.

The control needle 1256 extends past the end of barrel 1234 and passeswith several thousandths of an inch clearance through hole 1287 in block1260. This clearance provides for supercritical fluid flow from supplytubing (not shown) and through a conventional compression fittingconnector, not shown in FIG. 8, screwed into conventional femalecompression fitting 1282 for a 1/16" tubing connector.

To permit fluid flow, there are connecting annular clearance betweencontrol needle 1256 and hole 1237, the annular clearance between theinside diameter of barrel tube 1234 and the coaxial needle 1256. Theseprovide clearance for fluid flow from the fitting 1282 down to theregion of silver soldered joints 1280 and 1281. Past these joints, thefluid flows through the annular region between control needle 1256 andbarrel tip 1233, and between needle tip 1257 and barrel tip 1233, and onto the region of fluid restriction 1240.

Sealing around needle 1256 is effected by canted helicalspring-activated Teflon flanged seal 1262, available from Bal-SealEngineering Company, Inc. 620 West Warner Avenue, Santa Ana, Calif.92707-3398, U.S.A. The seal is captivated between block 1260 and sealretainer block 1261. Four screws, one of which is shown as 1269 in thefigure, clamp blocks 1260 and 1261 together through force exerted by thescrew heads upon support block 1263. These screws are #4X 3/4" capscrews. Seal 1262 prevents supercritical fluid from the port 1282 fromleaking away from the metering region 1240 and towards the adjustmentknob 1266.

The expansion of the supercritical fluid occurs essentially at thedischarge opening 1240 of the tip 1233, 1257, making the extent ofconduit exposed to expanded extraction fluid almost without length, sothe expansion occurs in contact with the collection solvent, and theanalyte precipitates from the extraction fluid directly into thecollection solvent. This improves collection efficiency and decreasesplugging.

Supercritical pressure is maintained down to the orifice or restrictionregion 1240 of the distal end of the barrel tip, which is inserted intoa collection solvent or collection vessel. The distance between thepoint of the needle tip 1203 and the recessed seat in the barrel tipforms a variable orifice at 1240 which controls the flow rate, and isadjusted using knob 1266.

For such adjustment, the control needle head 1265 is finely threaded,using 80 threads per inch. Rotating the knob 1266 threads the needle1256 up and down through action of female threads in the actuation nut1268 upon needle head 1265. The resulting vertical motion causes thespace between the end of the needle tip and the end of the barrel tip tovary, developing a variable orifice 1240. Expanded fluid is thendischarged directly into the collection fluid or into the collectionvessel. In this design, the entire needle and knob assembly (1257through 1266) rotates with respect to the barrel tip 1233.

The concentric arrangement of barrel 1233-1234 and needle 1256, 1257allow the probe of the apparatus to be made to any suitable length. Fiveor six inches is typical. Gross buckling of the needle due tocompressive loading is prevented by the inside diameter of barrel 1233,1234, which supports the smaller needle 1257, 1256. The barrelexperiences a tensile loading, counteracting the buckling tendency ofthe needle. These two components working in unison provide for amechanically stable probe, regardless of length.

The needle tip 1257 is preferably made of 17-7 PH stainless steel whichhas been hardened to CH900 which produces a strength of about 290,000pounds per square inch. The barrel tip 1233 should preferably be softerthan the needle tip, although still hard. A recommended material is type15-7Mo stainless steel hardened to RH950 which produces a strength ofabout 200,000 pounds per square inch. The needle tip 1257 is silversoldered to control needle 1256 at the region 1281. The distal region oftip 1257 is water cooled during this silver soldering process so thatthe heat from the soldering does not adversely affect its hardness.Barrel tip 1233 is silver soldered to barrel tube 1234 at region 1280.The pointed or distal end of barrel tip 1233 is water cooled duringsilver soldering to prevent the heat from adversely affecting itshardness.

The major outside diameter of barrel 1234 and barrel tube 1234 is 0.125"in the embodiment of FIG. 8. The inside diameter is 0.075" and length is6 inches. The diameter of control needle 1256 is 0.062" in theembodiment shown. The diameters of needle tip 1257 and barrel tip 1233are stepped down near their distal ends to provide more space for arestrictor heating element and thermal and electrical insulation aroundthe heating element. Following along the valve in the general directionof adjustment knob 1266, barrel tube 1234 progresses through electricalinsulator ring 1237, beyond which barrel holding flange 1236 is electronbeam welded to it.

The barrel tube 1234 may be made of 17-7RH stainless steel. Barrelholding flange 1236 may be made of type 303 stainless steel. Electricalinsulator ring 1237 is machined from polyetheretherketone plastic. Thebarrel tube 1234 ends inside of an extension of recess 1288 inconnection port block 1260. The four screws, one of which is indicatedat 1274, are each type #4-40X 3/8" cap screws, one of which is indicatedat FIG. 8. They captivate flange 1236 and barrel tube 1234 betweenbarrel holder block 1223 and connecting port block 1260. Gasket 1291, awasher of 0.010 inch thick 24k gold, effects a seal between flange 1236and block 1260 and prevents leakage of fluid.

The control needle 1256 is electron beam welded to needle head 1265 atregion 1259. Needle head 1265 carries fine, 80 thread per inch malescrew threads (1/4-80UNS), shown at 1264. These threads cooperate withfemale threads inside the central bore of actuation nut 1268. Actuationnut 1268 is made of Nitronic 60 stainless steel for resistance to wearand galling. Rotation of brass adjustment knob 1266 rotates needle head1265 and its threaded region 1264 because of the action of set screw1267 within the adjustment knob. Rotation of threads 1264 with respectto fixed threads and nut 1268 imparts reciprocating and rotating motionto control needle 1256 and its tip 1257. This provides adjustment of therestrictor orifice 1240 and therefore regulation of flow of fluidentering fitting 1282 and exiting the orifice 1240. Metal parts whosematerial is not otherwise indicated may conveniently be made of type 303stainless steel.

The seat in the barrel tip 1233 should be very hard, and the tapered tipof needle tip 1257 should be harder yet so that it does not deform or"ring". The needle tip 1233 may be made of type 15-7Mo stainless steelhardened to RH 950 (200 ksi tensile) and the needle 1257 may be made ofcold drawn 17-7RH stainless steel hardened to CH 900 (290 ksi tensile).Preferably the end of the outer wall 1202 of the barrel tip is coned forpunching through septum 1108 across collecting tube 37 (FIG. 7).

In FIG. 9 there is shown a partly broken away, partly sectioned view ofa variable restrictor forming a portion of the assembly of FIG. 8 and inFIG. 10 there is shown an enlarged fragmentary sectional view of therestrictor of FIG. 9. The needle tip 1257 shown in FIG. 8 is not shownin either FIG. 9 or FIG. 10 but a heater for heating the restrictor isshown comprising a winding 1201 of resistance wire 1243 that isconnected to the temperature control section 1015 (FIG. 8). This heateris used to electrically heat the barrel tip 1233 in the vicinity of theorifice or metering or restriction region 1240. The heating decreasesplugging at the orifice. The helical coil 1201 comprises approximately30 turns of resistance wire 1243 having a high temperature coefficientof resistance.

The wire 1243 is Pelcoloy (registered trademark of Molecu-Wire Company),0.004" diameter insulated with a polyimide coating with a thickness ofabout 0.00025". This wire is composed of 70% nickel and 30% iron and hasa temperature coefficient of +4,000 parts per million per degreecelsius. One end of the wire 1243 is resistance welded to the barrel tip1233 at location 1241. (FIG. 10). The other end of the coil is led upthe barrel and resistance welded at location 1235 onto step 1244 ofelectical connection ring 1238.

To insure a good thermal contact between the wire 1243 and the barrel,the barrel is first given a coating of uncured epoxy resin mix(Epoxylite Corp. type #5403) underneath the location upon which the wireis to be set. When the wire is wound on the barrel through the epoxyresin 1242, the epoxy resin fills all of the gap between the wire andthe barrel. The epoxy is also placed along the length of wire 1243 whichextends from the coil to the resistance weld at electrical connection at1235. Electrical connection ring 1238 lies on the step 1245 ofelectrical insulator ring 1237.

Ring 1237 is machined from polyetheretherketone plastic resin andinsulates the electrical connection ring 1238 from the barrel 1234. Theassembly as indicated is heated to 150 degrees Celsius to polymerize theepoxy resin 1242. The assembly as shown in FIG. 9 is placed in aconventional injection mold and 3/16 inch outside diameter plasticsheath 1239 is molded over the heating coil 1201 and the barrel 1234-235to provide both electrical and thermal insulation. A chemicallyresistant plastic resin is used for molding sheath 1239 so as also toprovide chemical resistance when the end 1240 is immersed deeply into acollecting liquid as shown in FIG. 7. Hoechst-Celanese VECTRA A115liquid crystal polymer is satisfactory for this purpose. Preferably thismolded assembly is stress-relieved at 250 degrees Celsius before use.

From FIG. 9 it is apparent that, if a voltage is applied betweenelectrical connection ring 1238 and barrel holding flange 1236, anelectric current flows through ring 1238, resistance weld 1235, wire1243, heating coil 1201, resistance weld 1241 (FIG. 10), barrel tip1233, barrel 1234 and flange 1236. This heats the barrel tip 233 in theregion of the metering restriction tip 1240, therefore heating themetering orifice and preventing the formation of either ice orprecipitated analyte. Preferably the heating is effected through atemperature controller which senses temperature by substantiallyconstantly monitoring the electrical resistance of the aforedescribedcircuit.

Most of the resistance of this circuit is within the heating coil 1201,and its large temperature coefficient of resistance is used to provide atemperature feedback signal through the variation of electricalresistance between the electrical connections at 1238 and 1236.

Temperature controllers which operate on the principle of sensing thetemperature of the heating element itself are described in Robert W.Allington U.S. Pat. No. 4,438,370 and in co-pending Daniel G. Jameson,et al. U.S. Pat. No. 5,268,103, the disclosure of which is incorporatedherein by reference. This method of temperature sensing is preferred toavoid the bulk and difficulty of thermal insulation and electricalconnection associated with the use of a thermocouple.

In FIG. 11 there is shown a schematic view of the temperature controlsection 1015 used to control the temperature of the variable restrictorand having for this purpose a four-pin connector plug 1229, two currentsupply leads 1221 and 1228, two voltage sensing leads 1246 and 1247,electrical conection lug 1227. The current supply lead 1228 and voltagesensing lead 1246 electrically connect the four pin connector plug 1229to the lug 1227 and the current supply lead 1221 and the voltage sensinglead 1247 connect the four pin connector plug 1229 to brass electriccontact ring 1225 (FIG. 8 and FIG. 11) The electrical conection lug 1227is screwed by screw 1270 (FIG. 8) to block 1263.

The four-pin connector plug 1229 is connected to the a controller withincomputer 2100 (FIG. 18) and the four leads 1228, 1227, 1246 and 1221 areused for heating current and the resistance (voltage) sensing accordingto the Kelvin method. To this end, leads 1228 and 1246 terminate inelectrical conection lug 1227 which is connected by screw 1270 (FIG. 8)to block 1263 which is in electrical contact with block 1261 which is inelectrical contact with block 1260 which is in electrical contact withblock 1223 which in turn is in electrical contact with flange 1260 whichis silver soldered to the barrel 1234. The other two leads, 1221 and1247, of connector plug 1229 are soldered at 1226 to brass electriccontact ring 1225 carrying setscrew 1222 which holds it in mechanicaland electrical contact with electrical connection ring 1238 which inturn is electrically connected to wire 1243.

A temperature controller within computer 2100 (FIG. 18) passes a currentthrough wires 1221 and 1228 and therefore through the heating coil 1201.The voltage developed across heating coil 1201 in response to thiscurrent is conducted to leads 247 and 246 and back to the sensing inputof the temperature controller.

As the temperature controller delivers the current through leads 1221and 1228 the heating element in 1201 increases in temperature andtherefore increases in resistance. This causes the voltage drop acrossit, which is brought through leads 1247 and 1246, to increase by adisproportionately larger amount. This is sensed by the controller todetermine the temperature of the heating element.

When the temperature of the heating element reaches the set pointtemperature of the controller, the controller decreases the currentthrough leads 1221 and 1228 and thereby regulates the temperature of theheating element to the desired amount. Electrical insulator block 1224covers and captivates contact ring 1225. Block 1224 may be machined fromultra high molecular weight polyethylene.

In FIG. 12, there is shown another embodiment of variable restrictor1018A having as its principal parts a body portion 1052A, an inlet port1050A, a heater 1080, a probe 1054A and a tip 1088. A Watlow Firerod(trademark of Watlow Electric co., 12001 Lackland Road, St. Louis, Mo.63146, U.S.A.) cartridge heater 1080, model C1E13 or similar is fittedinto a drilled hole in the body to maintain supercritical temperature inthe apparatus. These heaters operate on 24 V or 120 V, supplied throughwires 1082 and 1084. A 24 volt heater is safer. The cartridge suppliessupplemental heat when current is applied, providing additional heat tothe supercritical fluid so that it is kept at supercritical temperaturesin the extractor.

To control the temperature, a thermocouple (not shown) is mounted in ahole 1086 in the body, within 0.063" from the fluid path, and iselectrically connected to a temperature controller (not shown). Theheater is turned on and off by the temperature controller to maintainthe desired temperature as measured by the thermocouple. Heat istransferred from the cartridge to the valve body 1052A, and from thevalve body to the probe 1054A and to the fluid primarily by conduction.

The probe barrel tip end 1202 (FIG. 8) may be used as a variation of tip1088 and probe 1054A shown in FIG. 12. Tip 1088 and probe 1054A permitthe tip 1088 to be threaded into the probe 1054A and thus allow forrepair and replacement. The tip style 1088 results in a slightly longerdischarge conduit 1068A, but still is only about 3/16" long. Because ofits short length and its increasing diameter which enlarges from thevariable orifice to the surrounding outside region, the effect of theconduit is negligible. The mating orifice surfaces are sections of asphere, rather than zones as in FIG. 8.

In FIG. 13, there is shown, a still another embodiment of variablerestriction system 1018B adapted to be motor driven for automatedcontrol having an inlet port 1050B, a motor 1110, an encoder system1118, a probe barrel 1505, a movable needle 1504 and a partiallyspherical portion 1515 at the tip of the probe. Supercritical fluidcontaining dissolved analyte enters through port 1050B, with seal 1107preventing the loss of fluid along the needle. The port 1050B and seal1107 are identical to those in FIG. 8, items 1282 and 1286, but otherport configurations and seal designs would function equally well. Thesupercritical fluid then flows to the tip 1505 through the annular spacebetween the needle 1504 and the probe barrel 1504. The diameters of theneedle 1054 and barrel 1504 are the same as in FIG. 8. As was describedin FIG. 8, supercritical pressures are maintained up to the tip 1503 ofthe probe.

A 48 pitch, 40 tooth worm gear 1114, which in the preferred embodimentmay be purchased from Winfred Berg, is loosely positioned on the shaft1106. A 48 pitch, single start worm 1108 is attached to the shaft ofmotor 1110, which is a Lo-Cog (registered trademark of Pittman MotorCo., Harleyville, Pa. 19438-003) D-C Servo Motor, model 9413,manufactured by Pittman. This worm 1108 is engaged with the worm gear1104, so that the rotation of the motor armature 1112 causes the wormgear 1104 to rotate.

As the worm gear 1104 rotates in a first direction, it contacts pin1114, causing the threaded shaft 1106 to rotate also, opening therestrictor valve. An opposing torsion spring 1116 part number SPR3-5purchased from W. M. Berg, Inc. 499 Ocean Avenue, East Rockaway N.Y.11518, U.S.A. causes the shaft 1106 to rotate in the opposite directionwhen the motor 1110 is reversed, closing the restrictor. The torsionspring 1116 generates about 10 ounce-inches of torque when the valve isclosed.

When the restrictor properly closes by rotary force from the spring1116, pin 1114 separates from a slot in gear 1104. Motor 1110 drives thevalve open but can only permit it to close by spring force. Thisprevents the motor from driving the restrictor closed too tightly. Thedesign is motor to open, spring to close. A quadrature position encodersystem 1118 provides an electrical signal of motor rotor position andtherefore valve needle position.

The spring 1116 closes the restrictor, applying enough force at theclosed position to nearly stop the fluid flow, but not enough to causegalling of the needle tip 1515 or barrel tip 1503. The torsional springforce, working through the 5/16-48 cooperating threads 1120 in shaft1106 and packing nut 1109 generate a vertical force of about 23 poundson tip 1058B by the needle 1056B is provided to allow the needle 1504 tonot rotate independently of rotation of the shaft 1106, thereby reducingthe possibility of galling of the needle tip 1515 during closing.

Slip joint 1122 comprises a hard thrust ball 1124 located between thetop of a recess drilled in the bottom end of shaft 1106 and the top endof needle 1056B. This allows the shaft to force the needle down withoutrotating it. A loosely-fitting disk 1122 of stainless steel type 303with an outside diameter of 0.125" and a thickness of 0.063", silversoldered to the needle 1504 allows the shaft 1106 to raise the needle.

A hollow screw 1126 holds the disk in a matching hole in the end ofshaft 1106. A slight clearance (about 0.0005") between the disk 1122,the hollow screw and disc 1126 and the shaft 1106 allows the needle 1059to not rotate with respect to rotary motion of the shaft 1106, but doesnot allow significant vertical play. This creates a rotation slip jointat 1122, which prevents the needle tip 1515 from rotating with respectto barrel tip 1503 at full closure of the restrictor. Forced rotation ofthe needle tip 1515 with respect to the barrel tip 1503 when the needle1504 is closed results in wear and galling of the area where the needletip and the barrel tip contact.

Shaft 1106 is threaded with 5/16-48 UNS threads 1120, and the rotationof shaft 1106 in one direction moves the needle tip away from the barreltip. The shaft 1106 is threaded at 1120 into the packing nut 1109 of therestrictor, generating a vertical motion of the needle 1504 as the shaft1106 rotates. This vertical motion causes the spacing between the needletip 1515 and the barrel tip 1503 to change, resulting in a change in theorifice area which controls the flow. The threads 1120 are coated withan anti-seize lubricant or similar to prevent wear and galling of thethreads, which experience about 23 lbs. of axial loading in operation.

In FIG. 14, there is shown a block diagram of the restrictor and thecontroller for the restrictor. This controller may be used for controlof the motorized variable restrictor for automatic independent controlof the pressure within, and fluid flow rate through, an associatedsupercritical fluid extractor or supercritical fluid chromatograph. Inthis embodiment, the pump sets a constant pressure and the restrictorsets a constant flow.

The restrictor controller of FIG. 14 has a motor angular position setpoint signal generator 1152, a servo amplifier 1154, a restrictor-valvecontrol circuit 1156, an up/down counter and decoder, a subtractor 1142,a needle 1184 and a valve seat 1186. An Isco "D" series pump 1131 keepsthe system at constant pressure and the restrictor is servo-operated tomaintain a desired flow rate.

A flow rate feedback signal on the flow rate feedback conductor 1130 isread from the volume (piston displacement) sensor in the syringe pump1131. Thus, no gas flow rate measuring transducer is required at theoutlet. This pump piston feedback signal is subtracted from the flowrate set point signal on the flow rate set point conductor 1132 enteredby the operator in a signal subtraction circuit 1134. The result is aflow rate error signal on conductor 1136 (a difference) which isintegrated and multiplied by a constant K1 in multiplier 1138 and issent to a second subtraction circuit 1140 as a valve motor angularposition set point signal applied to input 1142 through a conductor1144.

The restrictor valve position is sensed by motor shaft position encoder1118, converted to motor position by quadrature detector/counter 1146and presented as valve motor position signal on conductor 1148.

The valve motor angular position signal on conductor 1148 is subtractedfrom the motor angular position set point signal 1142, resulting in avalve position error signal on conductor 1150. This signal is applied toa servo circuit 1154. An amount equal to the constant K2 times theposition error signal on conductor 1158, plus a constant K3 times therate of change of position error on conductor 1160, and plus a constantK4 times the integral of the position error on conductor 1162 is thennumerically summed in adder 1170 and the power amplifier 1176 iscontrolled based on this sum from 1170.

The power amplifier 1176, deriving power from power supply 1180, excitesthe valve motor 1178, causing it to rotate. A quadrature positionencoder 1118 attached to the motor shaft 1178, signals the currentposition and direction of rotation using two phase signals 1172 and1174. These signals 1172 and 1174 are measured by the quadraturedetector and up/down counter 1146, which provides the valve motorangular feedback signal 1148 to the position subtraction circuit 1140.

The motor 1178 is also attached to the mechanical drive 1182 that movesand positions the needle 1184 with respect to the seat 1186. This can beany mechanism that translates the rotational motion of the motor 1178into a position adjustment of the needle 1184, such as the mechanismdescribed above in FIG. 13.

In FIGS. 15 and 16, there is shown a front elevational sectional viewand a side elevational sectioned view of a motor controlled restrictoroperated by spring compression, but having substantially the sameprincipal parts as the embodiment of FIG. 13. Mechanically, the closingforce is supplied by spring compression, rather than by a torsionspring. In this arrangement, the needle 1190 can be positively preventedfrom rotating during closing, preventing destructive galling of theneedle tip 1192.

The opening motion is provided by motor 1178, a Lo-Cog (registeredtrademark of Pittman Motor Co., Harleyville, Pa. 19438-0003) D-C ServoMotor, model 9413, manufactured by Pittmann. Any suitable motor ormechanical device creating rotational motion at enough torque would workas well.

A 64 pitch, 11 tooth gear, supplied by Pittman attached to and part ofmotor 1178, rotates a 64 pitch, 192 tooth 200 pressure angle Delrin™(DuPont) spur gear 1196, purchased from Forest City Gear, part number69-0943-237. Spur gear 1196 is mounted to a support spool 1198, machinedfrom 17-4 PH stainless steel, hardened to Rockwell C42-48. Spool 1198 isthreaded onto 182FM (Carpenter Technologies) stainless steel shaft 1200with 5/16-48 UNS threads. The shaft 1200 is prevented from rotating byclamp 1202, which is held to the shaft by friction force created by a#4-40 cap screw 1204 (FIG. 16). The rotation of clamp 1202 is preventedby pin 1206, which travels in a slot 1208 in the support plate 1210. Therotation of spool 1198 results in a vertical motion of shaft 1200, whichpresses against the spring retainer 1212 at 1218, lifting the needle1190. The needle 1190 is attached to the spring retainer 1212 by acompression fitting (Vespel™ DuPont ferrule) 1214, which is compressedand held in place by compression nut 1216.

As the spring retainer 1212 is lifted by action of motor 1178, gear1196, spool 1198 and shaft 1200, the helical compression spring 1220 iscompressed. When this spring 1220 is compressed flat, the mechanismstalls the motor 1178, limiting the distance the needle 1190 can belifted.

When the motor 1178 is operated in the opposite direction, closing thevariable orifice 1192, the shaft 1200 is lowered, and the spring 1220force the needle 1190 downward. A type 316 stainless steel wear spacer1222 is used to prevent damage to the aluminum top block 1224 by spring1220. Once the variable orifice is fully closed, shaft 1200 separatesfrom the spring retainer 1212, and the variable orifice is held closedby spring force only.

When the orifice 1192 is fully closed, the spring 1220 is still somewhatcompressed, and hold the orifice 1192 closed with 20 to 40 lbs. offorce. As the motor 1178 continues to lower the shaft 1200, the shaft1200 contacts the seal capture nut 1217 at 1228, causing the motor 1178to stall. This limits the distance shaft 1200 can move downward,eliminating the need for shaft position switches.

The spool 1198 and gear 1196 assembly rotates freely on ball bearings1236, and is supported by spacers 1238 from the bearings 1236. Bearings1236 are lightly pressed into the support plates 1240 and 1242. Shaft1200 is about 0.001" smaller in diameter than the inner diameter ofbearings 1236, and can freely move vertically inside the bearing 1236.

The needle 1190 is attached to the spring retainer 1212 using acompression ferrule 1214 and nut 1216. This method allows the needle1212 to be positioned during assembly and adjusted if necessary. Theneedle 1212 is prevented from buckling in operation by being containedthroughout its length inside the spring retainer 1212, shaft 1200, sealcapture nut 1217 and probe 1234. Throttling of the supercritical fluidtakes place between the narrow coned end 1192 of the needle 1190 and abroader angled female cone in tip 1230.

Supercritical fluid enters the apparatus through a compression fittingport 1232, and flows in the annular space created by the probe 1234 andthe needle 1190. The fluid is prevented from flowing upwards along theneedle 1190 by the PTFE seal with canted coil backing spring 1248, typeX15829 made by Bal-Seal and described above. A 303 stainless steelbacking ring 1244 holds the seal 1248 in place in the body 1250, and isretained by a seal backing nut 1217. A 303 stainless ring 1246 issoldered to the probe 1234, and makes a metal to metal seal with thebody 1250 due to the compression action of the holding nut 1252.Optionally, a gasket washer can be incorporated to facilitate sealing.The fluid path formed is as small as possible, to reduce dead volumesand prevent the necessity of washing out the apparatus. None of thedrive components and anti-rotation features are in the fluid path.

The components of the apparatus are held together by two parallel sideplates 1210 and 1254. A spring support block 1224 transfers the springforce to the side plates 1210 and 1254, which transfers the spring forceto the spacer blocks 1276 and 1278 and body 1250. The probe 1234 isattached to the body 1250 with the holding nut 1252, and holds the tip1230. The spring force is transferred to the tip through this path, andresults in a tensile loading of the outer tube of the probe.

The upper end of the spring 1220 transfers the spring force to thespring retainer 1212, which transfers the force to the needle 1190through the compression ferrule 1214 held in place by the nut 1216. Thisresults in a compressive force on the needle 1190 that produces thetensile force in the probe 1234. The needle 1190 can be driven downwardsinto tight fit within the tip 1230 only through force from the spring1220. The motor 1178 can lift the needle away from the tip and againstthe springs. Force from the motor does not lower the needle, andtherefore the action of the valve is "motor-to-open/spring-to-close".This prevents damage to the end 1192 of the needle and to the seatwithin tip 1230. The motor position is sensed by encoder 1256. The motoris indicated as 1178 in FIGS. 14 and 17.

In FIG. 17, there is shown another automatic restrictor controlembodiment in which the pump sets a constant flow and the restrictorsets a constant pressure. The restrictor and restrictor controller havea motor angular position set point signal generator 1152, an up/downcounter 1188, a subtractor 1140, a servo amplifier 1154, a restrictorvalve control circuit 1156, a movable needle 1184, a valve seat 1186 anda pressure monitoring system 1262. The pump (not shown) driven by motor1178 supplies the fluid to the apparatus as a constant volumetric flowand the restrictor regulates the expansion process by controlling thepressure.

In cooperation with the circuit of FIG. 17, the pressure transducer 1016monitors pressure in tubing 1030 connected to the outlet ofsupercritical fluid extractor 1040 and in connecting tubing 1032upstream of the variable restrictor needle 1184 and seat 1186. Anelectrical signal from the transducer is carried on leads 1046 and 1048to signal amplifier 1264. The output of the amplifier on lead 1272 is apressure feedback signal. The pressure feedback signal 1272 issubtracted from a desired pressure set point 1270 using a subtractioncircuit 1134. The result is a pressure error 1274 signal, which ismultiplied at amplifier 1268 by a constant K5 and integrated at 1266.The outputs of amplifier 1268 and integrator 1266 are added together andcreate a valve motor angular position set point signal on lead 1142.This valve motor angular position set point signal is logically andfunctionally identical to the motor angular position set point based onflow rate 1142 (FIG. 14). The remainder of the control circuit is thesame as in FIG. 14, except that since the principal feedback is pressureinstead of pump piston displacement, the restrictor controls pressurerather than flow rate.

From the above description, it can be understood that the supercriticalextractor or supercritical fluid chromatograph of this invention hasseveral advantages, such as for example: (1) it reduces the amount ofsample that is coated onto the inside walls of the tubing; (2) itreduces the time and expense of removing contaminants caused by priorsamples from tubing; (3) it collects a large amount of sample,particularly by avoiding the escape of volatile sample; (4) it isparticularly adaptable to automatic operation of an extractor; and (5)it offers a restrictor that seldom clogs, either with ice or analyte.

In FIG. 18, there is shown a block circuit diagram of the controlcircuitry 2200 for gear motor 570 (FIGS. 4, 5 and 6) which operatessupercritical fluid supply valve 54 A (FIG. 6), gear motor 574 (FIG. 5)which operates extraction valve 50A (FIG. 5), and gear motor 573 (FIG.4) which then operates valve 52A (FIG. 4).

The control circuitry 2200 includes a programmer or other computer 2100,controlling a supply motor circuit 710, an extract motor circuit 712 anda vent motor circuit 714 to control the valves 54A (FIG. 6), 50A (FIG.5) and 52A (FIG. 4), respectively, a reversing switch 716, a drivecircuit 720 and a reverse motor torque circuit 718. The computer 2100 iselectrically connected to the supply motor circuit 710, the extractmotor circuit 712 and the vent motor circuit 714 through a conductors2118, 2119 and 2120 electrically connected to output terminals of thecomputer 2100.

The drive circuit 720 supplies power to a reversing switch 716 that isalso electrically connected to the supply motor circuit 710, the extractmotor circuit 712 and the vent motor circuit 714 to apply power to theselected one of those motors with a polarity that controls the directionof movement of the motors to open a valve or close a valve. Thereversing switch 716 is electrically connected to conductor 2122 from aport 2022 in the computer to activate the reverse direction for closingthe valve. This port is electrically connected to the reverse motortorque circuit 718 which controls the amount of torque in opening thevalve and is for that purpose electrically connected to the drivecircuit 720. A feedback circuit on conductor 2057 is electricallyconnected to the supply motor circuit 710, extract motor circuit 712 andvent motor circuit 714 to provide a feedback signal to the controllerwhich controls the stopping of the motor when the valves close fully.The stop motor signal comes from conductor 2121 from the port 2021 inthe computer or programmer 2100.

In the preferred embodiment, a programmable computer with timingcircuits is utilized. It is the same computer used to operate theembodiment of FIG. 3. However, a manual switch can be used instead whichswitch is connected to a positive voltage supply to energize thecorresponding motor when closed.

The control circuit 2200 includes a supply motor circuit 710, an extractmotor circuit 712, a vent motor circuit 714, a computer or programmer2100, a reversing switch 716, a drive circuit 720 and a reverse motortorque circuit 718. The supply motor circuit 710, extract motor circuit712 and vent motor circuit 714 open and close corresponding ones of thevalves 54A, 50A and 52A.

To control the valves, the computer or programmer 2100 has a pluralityof output conductors that determine which valve is to be moved and thedirection in which it is to be moved. This, in the preferred embodiment,is the computer which operates the extractor 10A (FIG. 3) but may be anytiming device or indeed, instead of a programmer, manual switches may beused to close circuits to 15-volt DC voltages to open and close thevalves as desired by an operator.

In the preferred embodiment, conductors 2118, 2119 and 2120 areconnected to outputs 2018, 2019 and 2020, respectively, of the computeror programmer 2100 and to corresponding ones of the supply motor circuit710, extract motor circuit 712 and vent motor circuit 714 to selectthose valves for opening or closing. A low-level signal on lead 2127attached to computer output port 2021 is electrically connected throughinverter 2026 to the drive circuit 720 to cause it to supply power tothe selected valve through the reversing switch 716 which iselectrically connected to the port 2023 through conductor 2123 to thereversing switch 716 and drive circuit 712.

The reversing switch 716 is electrically connected through conductors onthe same cartridge may be made by leaving the sample cartridge 30A inplace and advancing only the collection reel. The cycle of opening thevalves and extracting is then repeated until the number of extractionsfrom the single sample cartridge 30A (FIG. 3) have been made and theextractant deposited in a number of successive collection vials.

In FIG. 19, there is shown a schematic fluidic diagram of an automatedsupercritical fluid extraction system 10B similar to the supercriticalfluid extraction systems 10 (FIG. 1) and 10B (FIG. 3) having a pumpingsystem 814, a fluid-extraction assembly 878, and a collection system916.

To supply extracting fluid to the pumping system 814, the tank 802communicates with the pumping system 814 through tubing 952, a manualvalve 806 and a fitting 804 for the valve 806. The outlet of the valve806 is connected to the inlet port 812 of the pumping system 814 throughthe tubing 810 which is connected to the valve 806 by fitting 808 and tothe pump by another fitting not shown.

The outlet of the pumping system 814 communicates with thefluid-extraction assembly 878 through two different lines, the inletvalve system 956 (enclosed by dashed lines) and the wash valve system954 (also enclosed by dashed lines). The pumping system 814 alsocommunicates with the collection system 916 through the cooling valvesystem 958.

Prior to an extraction, a sample cartridege 870 is moved into thepressure chamber in the manner described above in connection with theembodiment of supercritical fluid extractor 10B (FIG. 3). The pumpsupplies clean extracting fluid from a source of extracting fluid to oneport in the breech plug assembly so that it flows adjacent to the sealsto clean them and out of the fluid extracting assembly 878. This fluiddoes not flow during extracting of a sample.

During an extraction the pump communicates with the sample cartridge 870located in the fluid-extraction assembly 878 through the inlet valvesystem 956. The fluid flow path goes from the pump to tee connector 820through tubing 960 which is connected by fittings 816 and 818. The firsttee 820 is connected to a second tee 842 through tubing 838 and fittings836 and 840.

One outlet of the second tee 842 is connected to anelectrically-actuated valve 850 by tubing 846 which is connected usingfittings 844 and 848. This electrically-actuated valve 850 is describedin U.S. Pat. No. 5,173,188 issued Dec. 22, 1992, form application Ser.No. 07/847,652, filed Mar. 5, 1992, in the names of Robin R. Winter,Robert W. Allington, Daniel G. Jameson and Dale L. Clay, the disclosureof which is incorporated by reference. The electrically-actuated valve850 is connected to the inlet housing 868 through a coiled heatexchanger 854 and fittings 852 and 866. In FIG. 19, this heat exchanger,actually located in a recess in aluminum temperature control jacket 966,is shown removed for clarity. A heating element and temperature-sensingthermocouple (neither are shown) are imbedded in the jacket 966. Aconventional temperature controller regulates the heating to control thetemperature of the jacket and therefore the temperature of extractionvessel 1042.

Pressurized supercritical CO₂ is heated in the heat exchanger 854 andenters the extraction vessel 1042 and the interior of the samplecartridge 870. This fluid entry is from the top of the extraction vesseland sample cartridge through an inlet housing as will be explained ingreater detail hereinafter.

The inlet housing splits the flow during the initial fill when thechamber is pressurized between the outside and the inside of cartridge870. The inlet housing is sealed to prevent leakage and to prevent fluidfrom communication with the surroundings. Inside the cartridge 870 is avoid space above the sample. After passing through the void space andsample the fluid enters a nozzle of the breech plug below the cartridge870.

During extraction there is no fluid flow in tubes 864 or 882 used toclean the breech plug seals as briefly described above. The fluid fromthe extraction cartridge enters an opening in the nozzle of the breechplug 1010 and proceeds up and around the upper seal and down and aroundthe lower of the seals that seal the breech plug to the pressure vessel.This design eliminates any dead space and, hence, extractant loss. Thefluid flow is sufficient to wash out the seals in less than a minutewith clean fluid.

A washout port is provided for this purpose. This port communicatesdirectly with the pumping system 814 through the wash valve system 954.This wash valve system 954 communicates with pumping system 814 throughthe second tee 842. This tee is connected to an electrically-actuatedvalve 860 by tubing 962 and fittings 858 and 856.

The connection from the valve 860 and the wash out port is provided by aheat exchanger 864 which is actually, physically, located in a recess(not shown) in aluminum temperature control jacket 966. This heatexchanger is connected by fittings 862 and 872. The heat exchanger ismade of 1/16" tubing with 0.005 I.D. This small inside diameter is toreduce the volume of the tube to minimize fluid and extract frombecoming trapped inside during the extraction cycle when the wash valveis closed.

During washing, valve 850 is closed and fluid in the radial passagewithin the breech plug 1010 is stationary. Fluid 1022 (FIG. 20) enteringthe wash port 1046 is directed to the same point 1024 that the fluidfrom the cartridge reaches just before it diverges to pass over theinner surfaces of the seals. From this point, whether the fluid is fromthe wash port or cartridge the flow path is the same. The fluid flowsthrough the seals in a split circular path as will be described betterin connection with FIG. 21. The fluid converges and exits through theoutlet port at fitting 874, the valve 904 and to the collection system.This washing takes place after each extraction to preventcross-contamination.

After the extraction is complete, valves 850, 860 and 904 are closed.The fluid in the pressure vessel chamber remains stagnant until thepressure is released by vent valve 894. This valve is anelectrically-actuated valve and is connected to the chamber throughtubing 882 with fittings 876 and 884, and to the over pressure safetydiaphragm 886 with tubing 890 and fittings 888 and 892. The fluid isthen routed away from the unit to a point of safe disposal throughtubing 898 which is connected to valve 894 by fittings 896. The fluidexiting the tube is a gas.

The fluid exiting the outlet port for extractant is routed to restrictor912 in the collection system 916. Located along this path is tubing 880which connects the outlet port to the electrically-actuated outlet valve906 through fittings 874 and 914. The fluid is then routed to a filter910 by tubing 908 which is connected using fitting 906. Fluid passesthrough the filter and then through the restrictor 912 which is insertedinto vial 914.

The extractant is partitioned within the collection solvent in the vial914 and the gas leaves through tubing 926. A septum retains gas pressurein the vial and the port maintains pressure with the backpressureregulator 920. A backpressure of greater than 20 psi prevents misting ofthe solvent. Misting will carry away and lose some of the analyte.

In FIG. 20, there is shown a fragmentary sectional view of the fluidextraction assembly 878 having as its principal parts the cartridge 870,an outlet port at fitting 876 connected to tubing 882, an extractingfluid inlet port fitting 866, a cleaning inlet port fitting 872 and apressure vessel cleaning fluid outlet port fitting 876.

In operation, pressurized supercritical CO₂ is heated in the heatexchanger 854 and enters: (1) the outer chamber space 1006 between thepressure vessel walls and the cartridge through tubing 1008; and (2) theinterior 1014 of sample cartridge 870. This fluid entry is through inlethousing 868.

The inlet housing 868 splits the flow during the initial fill when thechamber is pressurized. The flow is split between the outside 1006 andthe inside 1014 of cartridge 870. The flow splitter consists of achamber 1002 inside the inlet housing 868, a spring 1110, and a nozzle1004. The inlet housing 868 is sealed to prevent leakage and to preventfluid from communication with the surroundings by a washer seal 1112.

In the preferred embodiment, the seal is made from a soft metal such ascopper. The spring 1110 forces the nozzle 1004 against the cartridge andprevents direct communication of fluid between the inside 1014 and space1006 outside of the cartridge. However, during initial pressurizationthe nozzle 1004 splits the fluid flow between the inside and outside ofcartridge 870 by passing some of the fluid through its center and therest along slits 1004A along its length on the outside.

The point at which the fluid splits is in a small chamber 1002 locatedin the inlet housing. The fluid then passes between the nozzle 1004 andwasher seal 1112 before entering the chamber space 1006. The design issuch that the pressure between the inside and outside of the cartridgeis nearly equal at all times. Before and during extraction there is nofluid outflow through tubing 882. The fluid in the space 1006 is staticor stagnant during extraction.

Inside the cartridge 870 is a void space 1114 above the sample 1016.After passing through the void space 1114 and sample 1016 the fluidenters the nozzle 1030 of the breech plug 1010.

The breech plug assembly consists of the breech plug 1010, lower seal1026, seal spacer 1034, upper seal 1020, outlet port or point 1038 and aport tube 1012. During extraction there is no fluid flow in tubes 864 or882. The fluid from the extraction cartridge enters an opening in thenozzle 1030 of the breech plug 1010 and proceeds through the port tube1012 which is press fit into breech plug 1010.

The port tube 1012 transports the fluid to the center 1024 of the upperand lower breech plug seals 1020 and 1026. It also locks the orientationof the seal spacer 1034. There are two openings in the seal spacer, oneat the port tube 1012 and the other near the outlet port or point 1038.The fluid diverges at point 1024 into a four way split flowing up andaround the upper seal and down and around the lower seal. The sealspacer 1034 takes up the space between the seals, thereby forcing thefluid into the seals. This design eliminates any dead space and, hence,extractant loss. The fluid flow is sufficient to wash out the seals inless than a minute with clean fluid.

A washout port is provided for this purpose. This port communicatesdirectly with the pumping system 814 through the wash valve system 954(FIG. 19). This wash valve system 954 communicates with pumping system814 through the second tee 842. This tee is connected to anelectrically-actuated valve 860 by tubing 962 and fittings 858 and 856.

During washing, valve 850 is closed and fluid in passage 1044 isstationary. Fluid 1022 (FIG. 20) entering the wash port 1046 is directedto the same point 1024 that the fluid from the cartridge will reach justbefore it diverges to pass over the inner surfaces of the seals. Fromthis point, whether the fluid is from the wash port or cartridge theflow path is the same. The fluid flows through the seals in a splitcircular path as can be seen in FIG. 21 and converges at point 1034.From here it exits through the outlet port 1038 and to the collectionsystem. This washing takes place after each extraction to preventcross-contamination.

After the extraction is complete, valves 850, 860 and 904 are closed.The fluid in chamber 1006 remains stagnant until the pressure isreleased by vent valve 894. This valve is an electrically-actuated valveand is connected to the chamber through tubing 882 with fittings 876 and884, and to the over pressure safety diaphragm 886 with tubing 890 andfittings 888 and 892. The fluid is then routed away from the unit to apoint of safe disposal through tubing 898 which is connected to valve894 by fittings 896. The fluid exiting the tube is a gas.

The fluid exiting the outlet port is routed to restrictor 912 in thecollection system 916. Located along this path is tubing 880 whichconnects the outlet port to the electrically-actuated outlet valve 906using fittings 874 and 914. The fluid is then routed to a filter 910 bytubing 908 which is connected using fitting 906. Fluid passes throughthe filter and then through the restrictor 912 which is inserted intovial 914.

In FIG. 21, there is shown a sectional view through lines 21--21 of FIG.20 showing the seals between the breech plug 1010 and the extractionvessel 1042 and the wash or cleaning inlet port and outlet port atfittings 872 and 874 respectively. The arrows show the circulating ofthe wash fluid from point 1024 in counterclockwise and clockwisedirections between the upper and lower seals from the fitting 872 andout of the fitting 874.

In FIG. 22, there is shown a fragmentary sectional view of thecollection system 916 having as its principal parts a restrictor 912, asolvent 1442, a push tube 936, a vial 914, solvent port or tubing 926and septum 1418. The fluid containing extract flows through restrictor912 and exits as a gas at the bottom of vial 914. The expanded gasbubbles 1424 rise upward through solvent 1442 leaving the extract behindin the solvent.

The gas 1426 above the solvent continues rising and passes through aslit in the septum 1418. The septum is held to the mouth of vial 914 byvial cap 1420. The slit in the septum provides a passage for therestrictor. The septum is made of silicone rubber or other flexible,elastic material with a Teflon backing. The restrictor opens the slit inthe septum in such a manner that an opening is formed on both sides ofthe restrictor through which the gas exiting the vial passes. Gas entersa large opening 1438 in the vial guide 1432. The vial guide is sealedagainst the septum by spring 1416. The other end of spring 1416 isanchored to bottom piece 1422. The large opening 1438 is also sealed bya flange seal 1430 around the restrictor.

The restrictor 912 may be a capillary tube restrictor formed ofstainless steel tubing, available from Sterling Stainless TubeCorporation of Englewood Colo., or it may be a variable restrictor suchas shown in FIGS. 8, 12, 13, 15, 16, 28, 29, 30 or 31. Typical usefulsolvents are liquid dichloromthane and liquid isopropanol. The septum ismake of silicone rubber or other flexible elastic material with a Teflonbacking (Teflon is a trademark for tetrafluoroethyline fluorocarbonpolymers sold by DuPont de Numours, E. I. and Co., Wilmington, Del.,19898).

This design prevents the gas from communicating with the surroundings.The gas passes through tube 918 to a back-pressure regulator 920 (FIG.19). This regulator causes pressure to build inside the collection vialand decreases collection solvent and extract losses. Misting isessentially eliminated. Also, elevated pressure minimizes the violentbubbling that occurs and allows the amount of solvent to be measured.

A pressure of 40 to 50 psig is satisfactory, as are other pressures inthe range of 20 to 200 psi. The gas leaving regulator 920 is routed to aproper disposal point through tubing 922. Also, the vial guide isdesigned such that if the pressure exceeds a safe value the pressureforces vial guide 1432 up and breaks the seal. This prevents thepressure from exceeding the safety limit of the glass collecting vial.Nevertheless, the vial is located in an enclosure to decrease the riskdue to its shattering from the pressure. Control of collecting vesseltermperature by refrigerated bath and pressurizing the vessel to theextraction chamber pressure by multiple, mannually operated, needlevalves is described by Nam, et al. Chemosphere, 19, n. 1-6, pp. 33-38(1989). Nam does not disclose gassifying a supercritical fluid through arestrictor, nor settable or regulated control of collecting vesselpressure. Nam's system is not suitable for dynamic or flowingextractions.

Although the slitted septum 1418 is not entirely air-tight when the vial914 is lowered from restrictor 912 and placed in the vial rack (notshown), the septum substantially prevents evaporation of collectionsolvent and extract when the vial is in the vial rack. The slit tends tore-close.

If additional solvent is needed in the vial, some may be pumped in froma reservoir 932 using pump 928. The fluid is pumped from the reservoir932 through tubing 930 and then to the vial guide through tubing 926.The fluid enters the opening 1438 inside the vial guide 1432. It thenenters the interior of the vial through the same openings in the septumslit from which the gas escapes.

Elevated pressure and reduced temperature generally increases trappingefficiency. Therefore, a provision for precooling and maintaining thecollection solvent temperature is provided. Also, low collection solventtemperature may create a problem with restrictor plugging and iceformation.

In FIG. 23, there is shown a heating and cooling device 1631 having asits pricipal parts cooling lines 1614, 1648 and 832, blocks 1618 and1644 and electric heaters 1620 and 1642. The heaters and coolers arearranged to be selectively in thermal contact with the collection vial914.

For this purpose, lines 1614, 1648 and 832 communicate with the pumpthrough the valve cooling assembly 958 (FIG. 19). This assembly isconnected to the first tee 820. The connection is made by tubing 824which is attached to the electric valve 828 by fittings 822 and 826.This valve is then connected to another tee 1652 located above thecollection system.

This connection is made by tubing 832 and fittings 830 and 1654. Fluid834 enters tee 1652 and is split in two directions. The fluid then flowsthrough two restrictor cooling tubes 1614 and 1648 which are attached tothe tee by fittings 1612 and 1650. This pair of restrictors may be madeof a flexible material such as stainless steel capillary. Vaporizationof liquid CO₂ supplied by line 832 cools the collection vial 914 and itscontents. Each restrictor provides the same function to opposite sidesof the vial. Therefore, each component which controls the temperature ofthe vial is duplicated on either side.

The blocks 1618 and 1644 to which the restrictor cooling tubes arerouted, are spring-clamped onto opposite sides of the vial. These blocksare located in the collection system housing 1412. This housing ispreferably made of a non-heat-conducting material such as plastic. Eachblock is attached to the housing by spring pins, 1624 and 1638. Theopening in the block in which the pin passes through are slots. Thisallows the blocks not only to move toward and away from the vial but torotate as well. This allows the blocks to be forced out of the way bythe vial as it is lifted into position. The rotation makes it easier forthe blocks to clear the vial cap 1420 which is larger than the vial 914.Without rotation the blocks may bind when the vial is lifted.

The blocks 1618 and 1644 are forced against the vial by spring 1626 and1636. These springs are larger than the slots and are inserted in anopening in the side of each block and held in place by set screws, 1628and 1634. The blocks 1618 and 1644 are made from aluminum whichtransfers heat from the electric heaters 1620 and 1642 which are alsolocated in the blocks.

Heat is transferred by conduction from the heaters to the surface of thevial. The heaters 1620, 1642 and the CO₂ supply valve 828 are controlledby a conventional temperature controller equipped with a thermocouple(not shown) in thermal contact with liquid-filled portion of the vial914.

To cool the vial, the cooling lines are routed into openings 1656 and1658 in the blocks. These openings go all the way through the block andallow the cold CO₂, which exits the restrictor capillary tubing atpoints 1630 and 1632, to be directly against the vial. There are smallgrooves, 1622 and 1660, located along side of the blocks. They formpathways which guide the CO₂ along the sides of the vial to increasecooling. The CO₂ gas at points 1616 and 1646 is vented to thesurroundings and is driven away by natural or forced air convection.This produces the maximum amount of cooling in the least amount of timesince this technique does not require that the blocks be cooled beforevial cooling begins.

The vial 914 is raised by vial lift 942. This is best illustrated inFIG. 19. The gear motor 944 drives gear 946. This gear is attached tothe drive screw 940. The drive screw is held in place by bearing 948. Asthe drive screw rotates, rotational motion is translated into linearmotion by guide nut 938. This nut is attached to the push tube 936 whichin turn lifts the vial. The guide nut is prevented from rotating by theguide rod 952 which is anchored top and bottom. The push tube 936 isguided by a linear bearing 934.

After extraction, fluid is discharged from the chamber region 1006through tube 882, past overpressure blowout plug safety device 886,valve 894 which is opened at this time, and atmosphere vent tube 898.The blowout safety device 886 is always in communication with thechamber 1006, and incorporates a blowout disc that ruptures at apressure of 15,000 psi. This protects the extraction vessel 1042 (FIG.20) from dangerous rupture, as it is designed to hold a pressure inexcess of 70,000 psi. The normal maximum operating pressure within theextraction vessel 1042 is 10,000 psi.

In order to achieve down flow in the automated unit, the CO₂ inlet and aflow splitter must be relocated to the top of the chamber. These devicesmust fit within the confines of the upper section of the chamber and arecontained in an assembly which consists of an inlet housing, spring,nozzle and seal washer. This flow splitter assembly allows the pump tocommunicate with the inside and outside of the extraction cartridge. Thenozzle and spring are captivated in the housing by the seal washer andthe nozzle and spring are positioned as such that the spring forces thenozzle out of the housing and into the chamber.

When a cartridge loaded into the chamber compresses the nozzle back intothe housing, the force from the spring creates a seal between the nozzleand the cartridge. This prevents fluid in the outer chamber space 1006from entering the cartridge unless it diffuses through the tortuous pathback up around the outside of nozzle 1004.

The washer seal which holds the nozzle in place also seals the housingand prevents fluid from leaking to the outside environment. During anextraction, the fluid enters the housing 868 and flows through a pathwayto cavity 1002 where the spring and nozzle are located. From thiscavity, the fluid can communicate with either the cartridge or thechamber. The nozzle has a pathway through its center which directs fluidfrom the cavity to the inlet of the cartridge. Also, there is a slitdown the side of the nozzle which creates a pathway from the cavity tothe chamber. This design is such that the pressure will remain the sameinside and outside the cartridge when filling and during extractions.

After the fluid has passed through the cartridge, and hence the sample,it contains extract from that sample. The fluid must pass through anopening in the breech plug, flow across the seals and exit through theoutlet port. During extraction the seals are constantly swept byextraction fluid carrying progressively less and less extract. Thisprevents accumulation of extract on the seals. Therefore, this flow pathmust not have any dead space or stagnant regions.

To avoid dead space, the outlet port in the breech plug is oriented 180degrees from the outlet port of the chamber. This forces the fluid tosweep around the full circumference of the seals. There is a tube 1012pressed into the outlet port of the breech plug which directs the fluidto the center of the seals. The fluid is forced up into the seals by theseal spacer 1024 which is located between the seals 1020 and 1028. Thefluid diverges into four different directions and converges at thechamber outlet port.

To ensure that the seals are clean, a washout port is provided. Thisport communicates with the pump and delivers clean fluid to the samepoint that the outlet of the breech plug does. This clean fluid from thepump washes not only the seals but all the tubing including therestrictor which is located downstream.

The collection vial is lifted into the collection system assembly by thevial lift, cooled to a preselected temperature, and then heated orcooled (if necessary) to maintain that temperature. Also, the vial issealed such that pressure may be maintained and controlled in the vial,and gases are vented to a proper location.

The vial lift mechanism operates independently from the sample cartridgelift which allows vials to be changed at any time during or after theextraction process without depressurizing the extraction chamber. Thismechanism is driven by a gear motor and consists of the motor, drivescrew, guide nut, and push tube. The drive screw and guide nut convertsthe rotation of the motor to linear motion which then lifts the vial tothe collection assembly.

This collection assembly contains a vial guide, flanged restrictor seal,spring, stationary restrictor, and a collection system housing 1412. Therestrictor is anchored by block 1428 to the housing and is centered overthe vial. The vial guide is restrained by the assembly housing but isdesigned such that it may slide up and down its length. There is a largeopening in the guide that contains a flanged seal 1430 that therestrictor passes through as the guide moves. This seal and the sealprovided by the truncated cone 1440 bearing against septum 1418 preventcommunication of gases and vapors in the large opening with thesurroundings.

Before the vial is lifted up, the vial guide 1432 has been pulled nearthe bottom piece 1422 (FIG. 22) by the action of tension spring 1416.The vial first comes into contact with truncated cone 1440 located onthe vial guide. This cone enters the hole in the top of vial cap 1420and causes the vial to center itself on the vial guide before thestationary restrictor becomes inserted through the vial septum 1418.

The septum is held in place by a vial cap 1420 and has a slit whichallows the restrictor to pierce through and then close up when it isremoved. When there is no vial in the collection system, housing tensionspring 1416 pulls down vial guide 1432. The vial lift raises the vialuntil it contacts the lowered vial guide. Then it lifts both the vialguide and the vial until they have reached the proper location which iswhen the stationary restrictor is about 0.25 inches from the bottom ofthe vial, as shown in FIG. 23. The spring 1416 connected between theguide and housing forces the guide down onto the vial septum therebycreating a seal between the two. This seal and the seal 1430 around therestrictor allows pressure to build up in the vial.

The vial guide has 5 basic functions, which are: (1) it guides the vialto the proper position; (2) its spring forces the vial off of therestrictor and back into the vial rack when the vial lifter lowers thevial and this prevents the vial from catching in the collection assemblyif it is covered with frost due to cooling; (3) it seals against thevial septum to the truncated cone 1440 and around the restrictor andthis seal is capable of holding at least 50 psig; (4) it has a port foradding collection solvent to the vial; and (5) it has a port which ventsthe extraction gases and vapors.

The replenishment solvent port 926 intersects with the large opening1438, which the restrictor goes through, on the vial guide. Collectionsolvent is pumped into the vial through this port from a reservoir. Thesolvent passes through the port, the large opening and enters the vialthrough a gap in the septum. This gap is created on either side of theround restrictor when the restrictor is pressed through the pre-madeslit in the septum. The solvent is prevented from communicating with theouter environment by the seal between the septum and the vial guide, andalso the seal around the restrictor.

The vent port, which intersects the large opening, is connected to aregulator that controls the pressure inside the vial. The gases comingfrom the restrictor exit the vial through the same slit and gaps aroundthe restrictor that the solvent from the solvent port passes through.Then the gases pass through the large opening port and on to theregulator. From the regulator the gases and vapor are routed to a pointof proper disposal.

The temperature of the vial is controlled by heaters and CO₂ expansiondevices imbedded in two aluminum blocks. These blocks are spring loadedagainst the vial and are curved on the mating surface such that there isfull contact with the vial walls. Also, they are held in place by a pinanchored to the collection system housing. This pin passes through aslot in the blocks and a spring located between this pin and the blockis what forces the block against the vial. This pin and slot arrangementenables the blocks to float over the vial cap and vial by rotating aswell as move in and out.

The heaters imbedded into the block heat the vial by conduction throughthe aluminum block. The cooling lines, which communicate with either aCO₂ tank or pump, are inserted into an opening in each block whichpasses all the way through to the vial. This arrangement allows the CO₂to expand from the cooling lines and come into direct contact with thevial without having to cool the entire heating block first. The vialhousing, which contains the blocks, is made of plastic which resistsheat transfer thereby reducing the thermal mass which is heated orcooled to reach the desired temperature.

The parameters that are controlled for the extraction process includethe chamber and heat exchanger temperature, the collection solventtemperature and collection vial pressure, the extraction time andextraction pressure, the wash time and whether multiple vials are neededfor the extraction. A conventional microprocessor collecting controllerprovides all of the control functions.

Prior to the start of an extraction sequence, the valves, refill valve806, cooling valve 828, inlet valve 850, wash valve 860, and outletvalve 904 are closed. The only exception is the vent valve 894 which maybe left open for now.

If the pumping system 814 is empty, the refill valve 806 is opened toallow the CO₂ cylinder 802 to communicate with the pumping system 814.The pump is then activated to refill. When complete, refill valve 806 isclosed and pumping system 814 is switched to run and is pressurized tothe desired extraction pressure.

A vial 914 and cartridge 870 are lifted into position in the mannerdescribed previously. A sample cartridge 870 is lifted into position bycartridge elevator 808 which supports Nitronic 60® breech plug 1010. Thebreech plug is locked in place by a Nitronic 60 split locking bar 1048which locks and unlocks through motion perpendicular to the plane ofFIG. 20. The operation is similar to that of the locking mechanism of aWinchester model 94 rifle. The locking bar is captivated to theextraction vessel 1042 by slotted plate 1050. The plate 1050 and vessel1042 are made of 17-4 PH stainless steel hardened to H1050. The materialchoices of 17-4 PH and Nitronic 60 are made for strength, corrosionresistance and resistance to galling.

After the pumping system 814 is pressurized, the vent valve 894 isclosed and the inlet valve 850 is opened. The pumping system 814 nowcommunicates with the chamber 1042 and pressurizes chamber 1042, theinterior 1014, 1016 of cartridge 870 and its exterior 1006 through theflow splitter 1002, 1004, 1110.

While the chamber 1042 is pressurizing, the vial 914 may be cooled ifdesired. If so, the cooling valve 828 is opened allowing the pumpingsystem 814 to communicate with the cooling restrictors 1614 and 1648.The vial 914 will continue to be cooled until it reaches the selectedtemperature. At this time the heaters 1620 and 1642 may be turned on bytheir associated temperature controller to regulate this temperature,unless a very low temperature is selected.

When the pumping system 814 has pressurized the chamber 1042 to itsselected pressure, the outlet valve 894 is opened. The pumping system814 is now communicating with the restrictor and hence the vial 914. Thefluid flows through the heat exchanger 854, is heated to supercriticaltemperature, and enters the cartridge at a selected supercriticaltemperature. After passing through the sample 1016 the fluid proceeds tothe restrictor 912 through the breech plug 1010 and seals 1020 and 1026.At the vial 914 the pressure builds due to the pressure regulator 920located downstream of the vent port. When the preset, regulated pressureinside the vial is reached, the gas and vapors will proceed to adisposal point.

If during the extraction, additional collection solvent is needed in thecollection vial 914, a pump 928 is activated and fluid is pumped fromreservoir 932 to the vial 914.

This extraction process continues for the preselected time interval andat the end the process is either terminated and a new cartridge 870 andvial 914 are loaded or only vial 914 may be changed along with any ofthe extraction parameters such as temperature and pressure. If thelatter is chosen, the outlet valve 904 is closed and the wash valve 860is opened for a preselected interval. At the end of the wash interval,wash valve 860 and outlet valve 904 are closed and the vial 914 islowered and a new one inserted in a manner described previously. At thistime the outlet valve is reopened if all the parameters are stabilized.

When the sample cartridge has been extracted, a new vial 914 isselected, which may be a wash vial. A group of several wash vials may beused in sequence after each collecting vial. For each, the wash valve860 is opened for another preselected interval and the vial loading andunloading process is repeated until the new collection vial is loaded.The same group of wash vials can be used to wash all of the collectingvials because the dilution of contaminants is exponential for each washvial change.

After this cycle, when no further changing of vials is required, theoutlet valve 904 and inlet valve 850 are closed and the vent valve 894is opened for a length of time sufficient to vent the chamber. When thechamber is at atmospheric pressure the sample cartridge 870 and vial 914are unloaded and unit is ready for the extraction sequence to berepeated on another sample.

The embodiment of FIGS. 19-23 may be modified to provide a variablerestrictor similar to the variable restrictors of FIGS. 7-13. In such amodification, a probe assembly and point restrictor similar to thatdisclosed in FIGS. 8, 12, 13, 15, 16, 28, 29, 30 or 31 is used insteadof a restrictor tube such as the restrictor 912. In the preferredembodiment, a variable restrictor of the type shown in FIGS. 28, 29, 30and 31 is used.

In another modification the adjustable orifice at 1240 is formed andcontrolled differently so as to avoid the need for the needle tip 1257and the mechanism that adjusts its position with respect to the barreltip 1233 to control the pressure in the extractor, the tubing betweenthe extractor and the point restrictor and to control the rate ofrelease and the expansion of effluent into the collection environment.In this modification, the point restrictor is formed between the end ofthe probe and the adjacent surface of the collection container.

The rate of release of effluent is controlled by adjusting the distancebetween the end of the probe and the bottom wall of the collectioncontainer. This distance can be adjusted by moving the push rod 936 upor down as described in connection with FIGS. 19, 22 and 23 whileholding the probe stationary or by moving the probe such as with anelectromagnet or screw drive with respect to the bottom wall of thecollector container. The distance between the tip of the probe and thewall of the container controls the rate of release of the fluid from theprobe.

In FIG. 24, there is shown a block diagram of an interface and computercontrol system 2051 that measures and controls the temperature of aheater on a restrictor. One end of the heater is connected to the poweramplifier 2032 by a conductor 2034 through connector 2036. The computerdrives the power amplifier 2032 through D/A converter 2038. The outputcurrent from power amplifier 2032 flows through conductor 2034, throughthe electrical resistance provided by the circuit path through theheater 999, wire 2040, and through current sensing resistor 2042 to thepower return.

The voltage across the heater is amplified by a differential amplifier2044. The current through the heater generates a proportional voltageacross resistor 2042. This voltage is proportional to current and isamplified by differential amplifier 2046. The voltage and currentsignals are digitized by multiplexing A/D converter 2048 and transmittedto a computer 2050 which measures the voltage across and current throughthe heater. The resistance is then computed in the computer by division.The resistance relationship to temperature is described by equation 1,where R=heater resistance at temperature T, R_(O) =heater resistance at0° Centigrade, K=temperature constant for the heater wire, (K is about0.004 for type Pelcoloy (Molecu-Wire Co.). For a maximum overalltemperature range of 150° C., this reflects a 60% change in resistance.)

The temperature can then be calculated by equation 2.

The parameter R_(O) is measured automatically by the interface andcomputer control system 2051 of FIG. 24 at a known temperature such asat ambient temperature before the restrictor is heated. This is done bythe computer 2050 causing the digital to

    R=R.sub.O * (1+KT)                                         Equation 1

    T=(R-R.sub.O)/KR.sub.O                                     Equation 2

    R.sub.O =R/(1+KT)                                          Equation 3

    (K.sub.1 *V)-(K.sub.2 *I)=0 or V/I=K.sub.2 /K.sub.1 =heater resistanceEquation 4 ##EQU1##

    V.sub.2 =V* (R.sub.s /(R.sub.s +R.sub.t))                  Equation 6

analog converter 2038 and the amplifier 2032 to provide a very smallr.m.s (root mean square) voltage on conductor 2052. This allows theresistance measurement to be made without heating the restrictorappreciably.

If a fast A/D converter circuit is used, the voltage and currentmeasurements can be made during a voltage pulse having a duration thatis short compared to the thermal response time of the heater on therestrictor. In this case, the signal to noise ratio of the measurementsis improved by applying the full voltage available from power amplifier2032. The heating energy is low because the voltage is applied for onlya short time. After measuring the resistance R at any known temperatureT, R_(O) is calculated from equation 3.

When the barrel of the valve restrictor or the outer tube of thecapillary restrictor is used as the current return path, it and theresistance of conductors such as 3362 and 3363 (outside of the Kelvinconnections) connected to the barrel contributes to the totalresistance. Since the barrel of a valve restrictor may be at a differenttemperature than the heating coil at the orifice, its resistance and theresistance of any conductor lying upon it is not necessarily related tothe orifice temperature. Similarly, the outer tube of capillaryrestrictor is not necessarily at the same temperature as the restrictorcapillary. For most applications, it is not necessary to compensate forthe outer tube or barrel temperature. The barrel or outer tube has avery much larger conducting cross-sectional area than the heater and thelead conductor lying upon the barrel is short. For this reason, andbecause it is insulated in the middle and heated to the same temperatureat both ends, temperature variation of the barrel is not a significantfactor.

The closed-loop temperature control can be performed by several meanswhich control the output of the power amplifier driving the heater,whether wire or capillary. The power amplifier is adjusted to maintainthe heater resistance at a constant value and therefore maintain aconstant temperature. Although in the following implementations willemphasize the use of a valve restrictor with a heated orifice, thecomments also apply to capillary restrictor electrically heated alongits length. Three means (first to third) of implementing the control ofthe orifice temperature are as follows.

Firstly, a current sensing resistor is placed in series with the heater.The capillary current signal as sensed is amplified by this fixedresistor and the capillary voltage using separate gains which areopposite in polarity. The gains are chosen to balance the voltage signalwith the current signal at the desired capillary resistance. Animbalance (difference) is amplified by the power amplifier to heat theheater and maintain the desired resistance. Feedback is completed byamplifying a voltage corresponding to the error in heater resistance.

Secondly, the heater resistance is computed as the ratio of measuredvoltage divided by measured current and this value is used as thefeedback in a closed loop control system that maintains the heating wireresistance constant. The conductor resistance can be used to compute itstemperature as described above. The computed orifice heater temperatureis then used as the feedback signal in a closed loop temperature controlcircuit which accepts temperature as the control input and produces anelectric output that both electrically heats the orifice and providesthe measurement signals.

Thirdly, the orifice heater conductor is placed in one arm of aresistance voltage division circuit in series with a fixed resistor. Theratio of voltage across the orifice heater to the sum of voltages acrossthe heater wire and fixed resistor is maintained constant. This ineffect maintains a constant resistance ratio and therefore, a constantheater resistance. Feedback is completed by amplifying a voltagecorresponding to the error of heater resistance. The heater resistancecan be considered to be one of the four arms in a Wheatstone bridge.

In FIG. 25, there is shown a schematic of a circuit that may be used toprovide feedback control of the temperature of the restrictor orifice.This control method is similar to that described in U.S. Pat. No.4,438,370 and 5,268,103, the disclosures of which are incorporatedherein by reference.

With this circuit, the electrical power is applied to heater 2054 byservo-amplifier 2058. Current through heater 2054 is sensed by resistor3100 and amplified by an inverting differential amplifier composed ofamplifier 2060 and gain setting resistors 2062, 2064, 2066, and 2068which produce a voltage proportional to the heater current and oppositein polarity. The voltage across heater 2054 is amplified by anon-inverting differential amplifier composed of amplifier 2070 and gainsetting resistors 2072, 2074, 2076, and 2078. The output of amplifier2070 is applied to the reference voltage input of digital to analogconverter 2080.

Computer 2082, which controls converter 2080, selects the percentage ofvoltage at the output of amplifier 2070 to be applied to resistor 2084.The output of amplifier 2070 is also applied to resistor 2086. Resistors2084, 2086, and 2088 connect to the summing node 2092 of amplifier 2056.Resistor 2086 and resistor 2084 with the D/A circuit inject a positivecurrent into the summing node which is in variable proportion to theheater voltage. Resistor 2088 draws an opposing current from the summingnode which is proportional to the heater current.

When these two currents are balanced, the output of amplifier 2056 iszero. The current gain and the voltage gain determine the ratio ofheater voltage to heater current at which the summing currents willexactly offset each other. Resistor 2090 is connected to a negativevoltage -V to turn on amplifiers 2056 and 2058 when the apparatus isturned on. This prevents the circuit from hanging up before heatingstarts.

This is expressed mathematically in equation 4 in which V=voltage acrossthe heater, I=current through the heater, K₁ =voltage gain associatedwith amplifier, 2070, D/A 2080 and resistors 2086 and 2084, and K₂=current gain.

These equations show that the null point can be shifted to a new ratioof voltage to current: a new temperature, by changing either gain K₁ orK₂. In practice, it is only necessary to change one gain as the desiredheater resistance change is about 60 to 70 percent. Therefore, thiscircuit is designed to change the voltage gain over a range which willadjust the voltage/current ratio by about 60 to 70 percent. Resistors2084 and 2086 are chosen to set the fixed and variable gains to achievethis result. The variable portion of the voltage gain is set bymultiplying D/A 2080 with the set point provided by computer 2082.

If the heater temperature and therefore the heater resistance is lowerthan the set point, the positive current into summing node 2092decreases. In addition, if the output voltage from amplifier 2056 isconstant, the current through the heater increases due to the loweredload resistance. The increased current results in a larger current beingdrawn from summing node 2092 through resistor 2088. These two currentshifts both act to shift the voltage at summing node 2094 below thenon-inverting input of amplifier 2056. In response, the amplifier outputvoltage increases to balance the currents into and out of the summingnode.

The increased output voltage from amplifier 2056 drives servo-amplifier2058 which heats heater 2054, which will increase its resistance andrestore the voltage/current ratio selected by the computer. Amplifier2058 is designed to have a transfer function which provides stablecontrol of the heater temperature. A PID(Proportional-Integral-Derivative) transfer function of the typetypically used in control systems is suitable. This closed-loop controlsystem maintains the heater resistance, and therefore temperature at aselected value. Diode 2096 prevents reverse current flow through theheater wire 2054 if the temperature of the tube is higher than the setpoint value.

FIG. 26 is a schematic circuit diagram of a circuit useful incalculating the resistance of the heater for control purposes inaccordance with the embodiments of FIGS. 8, 9, 10, 15, 16, 22, 23, 28,29, 30 and 31. The heater current is sensed by resistor 2098 and scaledin magnitude by amplifier 2100 and gain-setting resistors 2102 and 2104.The heater voltage is amplified by a differential amplifier consistingof amplifier 2106 and associated gain-setting resistors 2108, 2110,2112, and 2114. The voltage signal conducted by conductor 2116 and thecurrent signal conducted by wire 2118 enter ratio circuit 2120 where asignal proportional to the voltage divided by the current is generated.The relationship of resistance to temperature is described by equation5, in which V=heater voltage, I=current through heater, R=heaterresistance at temperature T, R_(O) =heater resistance at 0° Centegrade,and K=temperature constant for the heater wire. (K is about 0.004 fortype Pelcoloy alloy. For a maximum overall temperature range of 150° C.,this reflects a 60% change in resistance.)

Computer 2122 generates a digital resistance set point which isproportional to the desired heater temperature. The resistance signal isconverted to a voltage by digital to analog converter 2124. Theresistance feedback signal from ratio circuit 2120 is subtracted fromthe resistance set point signal from D/A circuit 2124 by differentialamplifier 2126 and this difference or resistance error signal isamplified by power amplifier 2098 to heat the heater conductor 2128.

The resistor 2130 is led from a negative potential to the invertinginput of amplifier 2106 and resistor 2132 is similarly led to theinverting input of amplifier 2100 to insure turn-on of amplifier 2098when the apparatus is turned on. This prevents the circuit from hangingup before the heating starts. The amplification transfer function isdesigned to heat the capillary when the resistance, and therefore thetemperature, is too low. The transfer function of amplifier 2098 is ofthe usual proportional-integral-derivative (PID) type used in controlsystems. Diode 2094 illustrates that the control signal isunidirectional, or that it can only run current through the heater inone direction.

As the heater heats, its resistance increases until the voltage/currentratio matches the set point from computer 2122. This control systemfunctions as described to maintain a constant ratio of heater voltage toheater current and therefore a constant heater resistance. The theory ofoperation is the same as given in explanation of FIG. 24, and the sameequations apply. Elements such as the ratio computation, and othercontrol computations can be performed by a computer if one is present inthe system.

FIG. 27 is a diagram of implementation number three. The heater 2138 isconnected in series with current sense resistor 2134. The voltage V₂across resistor 2134 is equal to the output voltage of amplifier 2136multiplied by the ratio of resistor 2134 (R_(S) divided by the sum ofresistor 2134 plus the heater 2138 resistance (R_(t)) as shown inequation 6.

Set point voltage V₁ is generated by computer 2140 in conjunction withdigital to analog converter 2142. The reference voltage for the D/Aconverter is the amplifier voltage V (2149) or a voltage proportional toV. In this way, the output of the D/A circuit is equal to the digitalinput multiplied by the amplifier output voltage V. The D/A output isshifted and scaled by a level shift circuit composed of resistors 2144,2146, and 2148.

Since the heater resistance change over a typical operating temperaturechange of 150° C. is only about 60 to 70 percent, it is preferable toshift the D/A output and compress the full scale set point voltage V₁into the operating range of feedback signal V₂. The set point voltage V₁is a percentage of servo amplifier output voltage V with the percentagedetermined by the output of computer 2140. The voltage V₁ is subtractedfrom V₂ and amplified by a difference amplifier composed of amplifier2150 with resistors 2152, 2154, 2156, and 2158. The output current fromservo-amplifier 2136 heats heater 2138 so as to maintain the voltage V₂at the set point voltage V₁. Resistor 2160 is electrically connected topositive voltage V₃ to turn on amplifier 2150 and 2136 when theapparatus is turned on. This prevents the circuit from hanging up beforeheating starts. The amplified error signal is applied to heater 2138through diode 2160 to heat the heater.

As an example, suppose that the heater 2138 temperature is lower thandesired. The resulting resistance will be lower than the set pointvalue. As a result, voltage V₂ will be larger than set point voltage V₁.Amplifier 2136 incorporates the usual PID transfer function andamplifies the derived difference or error signal and heats heater 2138to increase its resistance and restore the balance between V₁ and V₂.

Although the restrictor valves described earlier are relativelyplug-free, they still tend to plug when extracting difficult samples.Perhaps the worst is elemental sulfur bearing samples such as certainriver sediments. Many other solid or semisolid analytes are also aproblem. A new valve of the preferred embodiment, which works very wellwith such difficult samples, will now be described.

In FIGS. 28, 29, 30 and 31, there are shown the valve restrictor,automatic restrictor or variable restrictor of the preferred embodiment.As best understood from these drawings, the restrictor operates asfollows.

When the valve is closed, the 45 degree included angle needle tip 3352is held against the valve seat 3314 under spring force generated byspring 3303, through ball 3304, bearing surface 3306, and needle or stem3308 which lies within tubular probe 3372. In this position, flow isstopped by closure of the valve seat 3314. Seat 3314 has a 45 degreeincluded internal angle, matching the external included angle of theneedle or stem tip 3352. Equal seat and needle tip angles provide morecontact area and therefore are relatively robust. The annular orifice3371 formed by needle tip 3352 and seat 3114, where fluid metering takesplace, is distanced from valve body 3312 by elongated barrel 3353, whichis the core of an elongated tubular probe 3372 with the valve controlbody 3312 and fluid inelt 3357 at one end of probe 3372, and the fluidmetering valve orifice 3371 in the opposite end of the probe. Therestrictor valve is shown opened in FIG. 29.

In this position, supercritical fluid is intended to enter the inlet3357 (FIG. 28), flow the length of the interior passage of tubular probe3372 and flow out the orifice 3371. When it is closed, needle tip 3352is flush with, or protrudes several thousandths of an inch from orifice3371. This prevents needle tip 3352 from pressing a ring-shaped stepinto the seat 3314. Gear 3309 is fastened to lift 3310. As servomotor3307 operates to open the valve, it rotates 11-tooth pinion 3351 (FIG.31), causing 192-tooth gear 3309 to rotate, which causes the tubularlift 3310 to unscrew because of external threads 3311 (FIG. 28)cooperating with internal threads in bushing 3368. This moves the lift3310 upward. Threads 3311 are fine threads, at least 20 threads per inchand 80 threads per inch in the preferred embodiment. The inside diameterof tubular lift 3310 is a slip fit on the needle 3308.

Assume to start that the valve is shut with needle tip 3352 in positivecontact with seat 3314. As the lift starts to move upward, the needle3308 is not coupled to the rotation of the lift, preventing galling ofthe needle tip 3352 in the seat 3314. As the lift continues to moveupward, it comes in contact with the cap 3350 of the needle 3308,causing the base to pull upward on the needle. As the top 3373 of thelift 3310 contacts the cap of the needle, the top of the lift imparts arotational friction torque on the needle. The top 3373 of the lift 3310is chambered to form a frustum of a cone. The resulting decrease inmaximum contact radius decreases the rotational torque to a desiredamount. Upward movement of the gear 3309 and lift 3310 decreases thedownward force of the needle tip 3352 against seat 3314, therebydecreasing the static friction torque between the needle tip and theorifice and between the side of needle 3308 and the inside wall ofbarrell 3353.

When the gear 3309 and lift 3310 rotate sufficiently further, therotational friction torque between lift 3310 and needle cap 3350 becomesgreater than the static frictional torque between needle tip 3352 andseat 3314 plus the static frictional torque between the side of needle3308 and the inside wall of metal barrel 3353. At this point, needle3308 rotates with gear 3309, assisting in smooth lifting motion of theneedle by breaking or scouring away analyte that may have depositedbetween tip 3352 and seat 3314, or between the side of needle 3308 andthe inside surface of metal barrel 3353. This is a self-cleaning actionthat takes place when there is little or no contact force between theneedle tip 3352 and the seat 3314, and therefore no damage to the needletip or seat. Flow regulation is accomplished by axially positioning theneedle by the motor driven lift. Note that the needle 3308 is notengaged in screw threads 3311, so screw thread friction does not affectthe precise positioning and application of force.

A conventional automatic restrictor valve with axial-only motion of thestem or needle has a tendency to pack or tamp deposited analyte into thevalve seat where it builds up and causes erratic or gross hunting motionof the servo-driven stem, producing erratic flow rates. The automaticrestrictor valve of the preferred embodiment has controlled rotarymotion of the stem due to frequent and minor servo adjustment actionwhenever the valve is partially open. This produces a scouring action onany deposited analytes so they do not build up on the seat. The resultis a much more constant and reproducible flow rate. Servomotor and servocontrol arrangements are described in accordance with FIGS. 1, 3, 14,15, 16 amd 17. Such arrangements control the extraction system pressureor flow rate or both by programming. Both pressure and flow rate changeduring a change in the pressure setpoint.

During closing, the needle rotates and moves downward with the liftuntil the tip 3352 contacts the seat 3314. The rotational (tangential)movement clears away deposited analyte that may be on the needle tip3352 or seat 3314. After further rotation, the static torque at theneedle tip exceeds the rotational torque at the needle base 3350 and thelift 3310 is no longer able to impart enough rotational torque on theneedle to turn it, preventing galling as the needle tip 3352 comes intopositive contact with the seat. The needle is held in a valve-closedposition by spring force exerted by spring 3303 through ball coupling3304 and 3306. This spring force may be between 10 and 300 pounds andpreferably is about 55 pounds. As the lift continues to move downward,only spring force is exerted on the needle, so damaging overclosureforce is not possible.

When the needle rotates, relative motion of the surface of the needletip 3352 with respect to the seat 3314 has a tangential (rotary)component of motion and an axial (opening or closing) component ofmotion. The mean tangential motion along the tapered tip should be atleast equal to the axial motion to provide adequate cleaning action. Inthe preferred embodiment, the mean tangential motion is about eighttimes the axial motion.

Optical sensor 3316 and flag 3317 attached to gear 3309 providereference position sensing for one rotation of the gear. Optical encoder3354 provides fine sensing of the shaft rotation of servomotor 3307,gear and lift position for feedback purposes (FIGS. 14 and 17), and hasa resolution greater than 1/50 of a revolution, and preferably issensitive to 1/2048 of a revolution. Position feedback is required forstable control of flow or pressure with the autorestrictor, and isimplemented as described earlier in this disclosure in connection withFIGS. 14 and 17. The resolution of the preferred embodiment is11/(192×80×2048)=0.35 microinch movement of the needle 3308. Theresolution is smaller than 40 microinches and preferably smaller than 5microinches. Gear 3309 is a precision gear and the position of the motoris adjusted to provide very low backlash between pinion 3351 and gear3309.

Regulated heating element 3355 heats the metal barrel 3353 near theorifice 3371 to prevent freezing of entrained freezable liquid due tocooling from CO₂ phase change or Joule-Thomson expansion and to at leastdecrease the tendency toward analyte deposition. The heater can heat theorifice to at least +30 degrees Celsius and preferably to +150 degreesCelsius. When a solvent trap is used, the orifice is immersed in themidst of the solvent so that no connecting tubing is used betweenorifice and solvent. Such connecting tubing is susceptible to plugging.The immersion of the orifice is enabled by locating the orifice on theend of a long narrow probe. The fluid conditions inside the probe aresupercritical so no analyte or frozen-liquid deposits occur. Withconventional orifice location on a valve body instead of in the probe, aconnecting tube would be necessary to extend the fluid path from theorifice into the midst of the trapping solvent. The pressure in thistube would be atmospheric, causing deposition problems and plugging.However, even with probe having a heated orifice at its tip, theself-cleaning action described above is still necessary, especially withproblem extractions, where all three of these features are necessary:scouring, heating and elimination of connecting tubing operating atatmospheric pressure.

Thermostat-controlled heating element 3356 heats valve block 3312, toprevent deposition in the valve block. Molded plastic sheath 3313electrically and thermally insulates barrel 3353 and heater 3315. Barrel3353 and sheath 3313 extend five inches from the bottom 3364 of valve ofthe probe 3372 and the outside diameter of the sheath is 3/16 inch. Theratio of barrel length to sheath diameter exceeds 4, and preferablyshould exceed 10. Barrell length should exceed 1 inch. The diameter ofprobe 3372 (including sheath, if any) should not exceed 0.5 inch. Thesebarrel dimensions and ratios also apply to the other elongated probeembodiments including those generally depicted in FIGS. 7, 8, 9, 10, 12,13, 15 and 16. In these foregoing embodiments as well as the preferredembodiment, the restrictor valve has an elongated fluid-conducting probewith a variable orifice at the distal end and means controlling theorifice at the proximal end of the probe.

Conductors 3362 and 3363 provide Kelvin-connections for a temperaturecontrol power supply and temperature self-sensing of high temperaturecoefficient heater 3355 as described earlier in regard to FIGS. 8, 9,10, 11, 24, 25, 27, and 28. The corresponding heater in FIG. 9 isidentified as 1201. In the preferred embodiment heater 3355 is doublepolyamide film insulated 0.004 inch diameter Pelcoloy (Molecu-Wire Co.)wire, and is placed on barrel 3353 as further described in conjunctionwith FIG. 9 and FIG. 10.

Inlet port 3357 is connected to the analyte outlet of a supercriticalextractor and feeds analyte plus supercritical fluid down into thenarrow clearance space between the needle 3308 and the inside of barrel3353, to the needle tip 3352. Upward fluid flow is prevented by seal3379. In the preferred embodiment, the main diameter of the needle 3308is 0.068 inch and the main inside diameter of the barrel is 0.075 inch.The main outside diameter of the barrel is 0.120 inch. The needle ismade of cold drawn 17-7RH stainless steel hardened according to CH900;producing a tensile strength of 290,000 psi. The barrel 3353 in theregion of the seat 3314 is made of 15-7 Mo stainless steel hardenedaccording to RH950; producing a tensile strength of 200,000 psi. Withregard to the seat and the needle, they are preferably not of the samehardness; the needle should be harder than the seat.

The narrow clearance between the needle 3308 and the bore of tubularbarrel 3353 is preferred because the needle is a buckled columnconstrained by the bore of the barrel. The needle assumes the shape of abow, with the point of maximum excursion rubbing against the inside ofthe barrel. The circumferential portion of the bow within the barrel isaffected by two opposing forces: 1) the tendency of the bow to orbit atthe same rate and direction as the rotation of the needle about its ownaxis, and 2) the effect of traction of the needle against the insidewall of the barrel tending to cause the needle to orbit in the oppositedirection. The side thrust and therefore the friction thrust of the bowin the high length-to-diameter ratio needle against the inside oftubular barrel is approximately proportional to the clearance. Theclearance is preferably 0.007 inch, earlier was 0.013 inch in a previousembodiment, and should not be greater than 0.030 inch. In a previousembodiment the needle and barrel walls were rough, producing a large anderratic coefficient of friction.

In the preferred embodiment, effort has been made to reduceneedle-to-barrel wall friction coefficient to improve flow stability.Effort also has been put into making the coefficient uniform. The barrelhas a smooth inside finish, better than 16 microinches rms andpreferably 8 micorinches. The needle is polished to at least 16microinches rms surface finish, and preferably 8 microinches, and thenis plated overall, sides and tip, with 0.0005 inch thickness of hardgold to provide low friction.

Fine finishes and gold plating on the side of the needle as well as onthe needle tip improves performance, as side thrust forces of the bowedneedle against the inside of the barrel are calculated to be low, on theorder of 0.7 pound in the previous embodiment with 0.013 inch clearancebetween needle and barrel. Friction was also low, but was found toproduce the erratic behavior in the adjustability of the valve. Theimprovement in adjustability because of closer clearance, finer finishesand gold plate may be due to lessening of stick-slip friction effectwhich irregularly causes frictional tractive forces on the stem as itbows and orbits against the barrel, followed by sudden loss of tractionand change in orbital position of the bowed stem within the barrel, as acontinuous and smooth change in adjustment is made. Another possibilityis that the point of maximum bow in the needle scuffs irregularly in theaxial direction along the inside wall as the needle is adjusted axially.The preferred low and uniform friction coefficient and decreased thrustwill greatly decrease this problem, too.

FIG. 30 is a top view of FIG. 28 and shows the relative positions of themotor 3307 and 192 tooth gear 3309. In FIG. 31, there is shown aschematic side view illustrating the operation of the restrictor. Beforeoperation starts, the lift guide 3335 is at the bottom of vertical lifttrack 3337. In operation, elevator 3390 carrying thermocouple 3391 liftsa collection vial 3330 with a cruciform-pierced or slitted rubber septum3324 held by plastic cap 3348 upward from under the orifice 3314 of thebarrel so that the orifice, then the barrel, and then makeup trappingsolvent supply tube 3361 thread through the pre-pierced septum. Septum3324 is made of rubber with a thin, bonded PTFE film on the side towardthe solvent 3331. For good re-closure properties, the rubber mustcontribute much more stiffness to the septum than does the PTFE film.Tube 3361 is coaxially disposed outside barrel shield 3313 and there isan annular makeup fluid flow space between them.

As the vial 3330 is lifted it raises the lift guide 3335 to the raisedposition shown in FIG. 31. The vial is filled to the desired level oftrapping solvent 3331. With the collection vial completely lifted, theseptum 3324 is pressed against the nose piece 3334 by spring 3370,creating a sufficient seal for over 40 psi. At a pressure above thesealing pressure, the spring stretches further causing nose piece 3340to lift and act as a safety valve. The cruciform-pierced slits (notshown) cut in the septum allow the gas to escape upward along the outersurface of tube 3361, through an annular flow space between tubes 3360and 3361, and out through port 3359, as shown by path 3382. Pressure isregulated to about 30 psi gauge with an external pressure regulator3367. The minimum advantageous pressure is 15 psi gauge. Leakage of gasaround the outside of vent tube 3360 is prevented with an O-ring 3349.

The coaxial vent tube 3360 does not press through the septum, becauseits diameter is large enough to significantly deform the septum, so thatit will not re-close. The trapping solvent is cooled by directing liquidCO₂ through cooling expansion lines 1614 and 1648 (FIG. 23) onto thelower part of vial. The temperature of solvent 3331 is cooled undercontrol by a CO₂ valve and temperature controller (not shown) connectedto thermocouple 3391 (FIG. 31).

In operation, the distal (variable orifice) end 3371 (FIG. 29) of theelongated probe 3372 (FIG. 28) extends below the surface 3373 (FIG. 31)of trapping solvent 3331.

The orifice 3371 is substantially surrounded by the trapping solvent3331. Surrounding of the orifice with the trapping medium providesimproved collection efficiency whether the trapping medium is a solvent,absorbent particles or inert cryotrapping particles. Cooling andpressurizing the trapping medium in collecting vial 3330 further provesthe collection efficiency. The trapping medium should be coolable to +5degrees Celsius and preferably to -20 degrees Celsius. Such temperaturecontrol is particularly important because the heated orifice 3371 isimmersed in the trapping medium. In the case of a solvent trap, thesolvent does not actually contact the flow metering passage of theorifice because of the gas flow leaving the passage, but heat conductionstill takes place. Temperature control and pressurization of acollection vessel to a pressure equal to the extraction chamber pressureis disclosed in Nam, et. al, Chemosphere, 19, No. 1-6 pp 33-38 (1989).Nam does not disclose gassifying a supercritical fluid through arestrictor, nor regulated control of collecting vessel pressure nor theheating of a restrictor. Neither is there disclosure of an insulated,variable nor automatic restrictor. Nam's system is for staticextractions and is not suitable for dynamic or flowing extractions.

Vent port 3359 (FIG. 28) is connected to the annular flow space insidetube 3360 and make up Solvent make-up port 3358 is connected to theannular flow space inside tube 3358. In a following step of operation,analyte and supercritical fluid pass into port 3357 and out the spacebetween needle tip 3352 and seat 3314. Refer to FIG. 31. Thesupercritical fluid gassified at the orifice 3371, passes throughtrapping solvent 3331 as gas bubbles 3332 which pressurize thecollecting tube 3330. Analyte entrained in the gas dissolves in thetrapping fluid as the bubbles pass upward. The gas rises above thesolvent 3331, passes through the slits in the septum 3324, into theannular space under tube 3360 and is discharged through port 3359.Pressurization of the collection vial by back pressure regulator 3367prevents misting of solvent which would carry off analyte in thedroplets of mist.

If the collecting vial is used as a solvent trap as shown, some of thesolvent may evaporate and also be carried out vent port 3359. To keepthe solvent level in the vial constant, a conventionally programmedsupply of make-up solvent (not shown) is fed into make up solvent port3358 and discharged into the collecting tube through the annular orificeinside tube 3361. Extraction and collection conditions may readily becontrolled well enough to insure the run-to-run reproducibilitynecessary to keep solvent level constant with preprogrammed, open loopsolvent addition control. An absorbent or cryogenic trap may be used inplace of solvent 3331 in vial 3330.

In any case, during trapping of analyte, variable orifice 3321 at theend of barrel 3353 is in the midst of the trapping medium whether suchmedium is solvent, absorbent or inert cryotrapping material. Thevariable orifice is in the midst of the medium as opposed to not beingburied well within the medium. Specifically "midst of the medium" meansthat the distal end of elongated probe carrying the variable orificeenters and protrudes into the trapping medium, and penetrates to a depthgreater than one-half of the distance from the point of entrance to thecenter of the medium. This improves collection efficiency. Such orificelocation also applies to the embodiments of FIGS. 7, 8, 9, 10, 12, 13,15 and 16.

During extraction the motor operates the valve under servo control tomaintain a preset flow rate regardless of pressure variations, or tomaintain a predetermined pressure for the supercritical extractionregardless of flow rate changes. At the end of extraction vent valve3320 connects atmospheric vent 3321 to vent port 3359, discharging thepressure in vial 3330. After a short wait for equilibrium, the vial 3330contaiing collected analyte is lowered and removed. The cruciform slitsin the septum 3324 re-close when vial 3330 is withdrawn from probe 3372,resealing the vial 3330.

In general, particulate-filled absorbence traps and cryotraps do notperform well when the supercritical fluid extractant contains a liquidmodifier or co-solvent. This is because the modifier liquid fills theinterstices between absorbent or cryotrapping particles, decreasingtheir surface area and the collection efficiency. The problem is worsewith absorbent traps as the modifier inactivates the absorbent, furtherdecreasing the collection efficiency. Solvent traps do not have thisdisadvantage as the modifier dissolves in the trapping solvent withoutdegrading its trapping properties.

Heretofore, solvent traps have been considered less desirable thanabsorbent traps because of: (1) the conflicting nature of ways toameliorate plugging and to improve collection efficiency as describedherein, and (2) the difficulty of automation of trapping with a solvent.

The invention is particularly advantageous when practiced with a solventtrap. A variable restrictor with a tubular probe separating its inletand control means from its restrictor valve orifice allows the orificeto be dipped directly into the solvent to provide high collectionefficiency without connecting tubing that would be subject to plugging.Controlled scouring means in the valve prevents it from plugginginternally, and without damage to itself. A heater heats the orifice toovercome cooling due to phase change or Joule-Thomson expansion of theextracting fluid to a gas and thereby to decrease and soften incipientdeposits. Cooling of the collection solvent overcomes thesolvent-heating effect of the orifice heater and further cools thesolvent to improve the trapping of volatile analytes. Pressurization ofthe collection vessel improves collection efficiency by furtherdecreasing loss from vaporization of analyte and preventing the mistingof trapping solvent which would carry off dissolved analyte. A detaileddescription is given of means for automating the entire process ofsupercritical extraction including an improved restrictor and solventtrap.

As can be understood from the above description, the supercriticalextraction technique has several advantages, such as for example: (1) itautomates the sample injection and fraction collection part of theextraction process as well as automating the extraction itself; (2)provides a superior solvent trap that performs better than previoussolvent, absorbent or cryotraps; (3) it provides improved trappingefficiency; (4) it provides low extract/solvent losses; (5) iteliminates analyte deposition, freeqing and plugging of the restrictor;(6) it provides constant and reproducible flow of the extractant forreproducible extractions; (7) it permits the conditions of theextraction, such as temperature and pressure, to be changed so as toremove certain substances from the sample matrix and deposit eachsubstance in a separate vial; (8) it is also useful for investigatingextraction kinetics by changing the vial during the extraction forexamination; (9) it permits the use of different size vials because thestroke of a lift is no longer tied to the extraction cartridge elevator;and (10) it permits the use of multiple wash stations to clean theoutside of the restrictor.

Although a preferred embodiment of the invention has been described insome detail, many modifications and variations of the preferredembodiment can be made without deviating from the invention. Therefore,it is to be understood that within the scope of the appended claims theinvention may be practiced other than as specifically described.

What is claimed is:
 1. A method for supercritical extraction orchromatography having an effluent with dissolved solid or semisolidanalyte or an entrained freezable liquid including the stepsof:providing a fluid pressurizing means, and a separation means with anoutlet for said effluent; providing a restrictor valve having an inlet,an adjustable metering stem and a seat, wherein the restrictor valve,the adjustable metering stem and the seat have the same axis; connectingthe inlet of the valve to the outlet; maintaining back pressure andenabling separation in the separation means by partially opening thevalve and producing a flow of said effluent exiting said valve throughan outlet orifice; providing servo means which controls either saidpressure or said flow or both with a servomotor that controls theadjustable metering stem; preventing objectionable deposit of saidanalyte or said freezable liquid in the frozen state on said seat orstem by employing a scouring means inside the valve which scours awaysaid deposited analyte or said frozen liquid when the valve is partiallyopen, and; preventing said scouring means from damaging either the seator the stem when the valve is brought to the closed position.
 2. Themethod of claim 1 where the scouring means is deactivated when the valveis closed.
 3. The method of claim 1 wherein the servomotor providesenergy to operate the scouring means.
 4. A method according to any ofclaims 1, 2 or 3, including the step of engaging the scouring means withan engaging means when the valve is partially open and disengaging thescouring means when said valve is closed.
 5. The method according toclaim 4 wherein the engaging means includes a rotary driving member, arotary driven member connected to the stem and an engaging means furthercomprising the steps of:connecting said rotary driving member to arotary adjustment shaft extending to an automatic rotary control meansout of contact with said effluent; activating said engaging means toconnect the rotary driving member to the said rotary driven member whenthe engaging means is activated and disconnecting the rotary drivingmember from the rotary driven member when the engaging means isinactivated wherein said engaging means is activated when the said valveis either open or partially open, and said engaging means is inactivatedwhen the said valve is closed.
 6. The method according to any of claims1, 2 or 3 wherein the seat is part of the outlet orifice and the outletorifice is located at the surface of the valve; said method furtherincluding the steps of trapping analyte entrained in gas exiting theorifice; said step of trapping analyte comprising the step of trappinganalyte in a trapping medium contained in a trapping means having anentrance means for said gas and analyte adjacent to the orifice.
 7. Themethod of claim 1 including the steps of:providing an elongated tubularprobe which separates the inlet and the servomotor from the valve andwhich fluidly connects the inlet to the valve; immersing and surroundingthe outlet orifice in a trapping medium, and; locating the servomotoroutside of the trapping medium.
 8. The method of claim 7 including thesteps of:providing heating means that heats the outlet orifice;providing a trapping solvent cooled by a cooling means for use as thetrapping means, and; immersing the heated outlet orifice into the cooledtrapping solvent.